Revert of Combine webrtc/api/java/android and webrtc/api/java/src. (patchset #1 id:1 of https://codereview.webrtc.org/2111823002/ )

Reason for revert:
Breaks downstream dependencies

Original issue's description:
> Combine webrtc/api/java/android and webrtc/api/java/src.
>
> It used to be that there was a Java api for devices not running Android
> but that is no longer the case. I combined the directories and made
> the folder structure chromium style.
>
> BUG=webrtc:6067
> R=magjed@webrtc.org, tommi@webrtc.org
>
> Committed: https://chromium.googlesource.com/external/webrtc/+/ceefe20dd65387d83059d9fc1ce84842650ed5e2

TBR=magjed@webrtc.org,tommi@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=webrtc:6067

Review URL: https://codereview.webrtc.org/2106333005 .

Cr-Commit-Position: refs/heads/master@{#13357}
diff --git a/webrtc/api/java/jni/classreferenceholder.cc b/webrtc/api/java/jni/classreferenceholder.cc
new file mode 100644
index 0000000..3d8f304
--- /dev/null
+++ b/webrtc/api/java/jni/classreferenceholder.cc
@@ -0,0 +1,137 @@
+/*
+ *  Copyright 2015 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+#include "webrtc/api/java/jni/classreferenceholder.h"
+
+#include "webrtc/api/java/jni/jni_helpers.h"
+
+namespace webrtc_jni {
+
+// ClassReferenceHolder holds global reference to Java classes in app/webrtc.
+class ClassReferenceHolder {
+ public:
+  explicit ClassReferenceHolder(JNIEnv* jni);
+  ~ClassReferenceHolder();
+
+  void FreeReferences(JNIEnv* jni);
+  jclass GetClass(const std::string& name);
+
+ private:
+  void LoadClass(JNIEnv* jni, const std::string& name);
+
+  std::map<std::string, jclass> classes_;
+};
+
+// Allocated in LoadGlobalClassReferenceHolder(),
+// freed in FreeGlobalClassReferenceHolder().
+static ClassReferenceHolder* g_class_reference_holder = nullptr;
+
+void LoadGlobalClassReferenceHolder() {
+  RTC_CHECK(g_class_reference_holder == nullptr);
+  g_class_reference_holder = new ClassReferenceHolder(GetEnv());
+}
+
+void FreeGlobalClassReferenceHolder() {
+  g_class_reference_holder->FreeReferences(AttachCurrentThreadIfNeeded());
+  delete g_class_reference_holder;
+  g_class_reference_holder = nullptr;
+}
+
+ClassReferenceHolder::ClassReferenceHolder(JNIEnv* jni) {
+  LoadClass(jni, "android/graphics/SurfaceTexture");
+  LoadClass(jni, "java/nio/ByteBuffer");
+  LoadClass(jni, "java/util/ArrayList");
+  LoadClass(jni, "org/webrtc/AudioTrack");
+  LoadClass(jni, "org/webrtc/Camera1Enumerator");
+  LoadClass(jni, "org/webrtc/Camera2Enumerator");
+  LoadClass(jni, "org/webrtc/CameraEnumerationAndroid");
+  LoadClass(jni, "org/webrtc/DataChannel");
+  LoadClass(jni, "org/webrtc/DataChannel$Buffer");
+  LoadClass(jni, "org/webrtc/DataChannel$Init");
+  LoadClass(jni, "org/webrtc/DataChannel$State");
+  LoadClass(jni, "org/webrtc/EglBase");
+  LoadClass(jni, "org/webrtc/EglBase$Context");
+  LoadClass(jni, "org/webrtc/EglBase14$Context");
+  LoadClass(jni, "org/webrtc/IceCandidate");
+  LoadClass(jni, "org/webrtc/MediaCodecVideoEncoder");
+  LoadClass(jni, "org/webrtc/MediaCodecVideoEncoder$OutputBufferInfo");
+  LoadClass(jni, "org/webrtc/MediaCodecVideoEncoder$VideoCodecType");
+  LoadClass(jni, "org/webrtc/MediaCodecVideoDecoder");
+  LoadClass(jni, "org/webrtc/MediaCodecVideoDecoder$DecodedTextureBuffer");
+  LoadClass(jni, "org/webrtc/MediaCodecVideoDecoder$DecodedOutputBuffer");
+  LoadClass(jni, "org/webrtc/MediaCodecVideoDecoder$VideoCodecType");
+  LoadClass(jni, "org/webrtc/MediaSource$State");
+  LoadClass(jni, "org/webrtc/MediaStream");
+  LoadClass(jni, "org/webrtc/MediaStreamTrack$State");
+  LoadClass(jni, "org/webrtc/Metrics");
+  LoadClass(jni, "org/webrtc/Metrics$HistogramInfo");
+  LoadClass(jni, "org/webrtc/NetworkMonitor");
+  LoadClass(jni, "org/webrtc/NetworkMonitorAutoDetect$ConnectionType");
+  LoadClass(jni, "org/webrtc/NetworkMonitorAutoDetect$IPAddress");
+  LoadClass(jni, "org/webrtc/NetworkMonitorAutoDetect$NetworkInformation");
+  LoadClass(jni, "org/webrtc/PeerConnectionFactory");
+  LoadClass(jni, "org/webrtc/PeerConnection$BundlePolicy");
+  LoadClass(jni, "org/webrtc/PeerConnection$ContinualGatheringPolicy");
+  LoadClass(jni, "org/webrtc/PeerConnection$RtcpMuxPolicy");
+  LoadClass(jni, "org/webrtc/PeerConnection$IceConnectionState");
+  LoadClass(jni, "org/webrtc/PeerConnection$IceGatheringState");
+  LoadClass(jni, "org/webrtc/PeerConnection$IceTransportsType");
+  LoadClass(jni, "org/webrtc/PeerConnection$TcpCandidatePolicy");
+  LoadClass(jni, "org/webrtc/PeerConnection$CandidateNetworkPolicy");
+  LoadClass(jni, "org/webrtc/PeerConnection$KeyType");
+  LoadClass(jni, "org/webrtc/PeerConnection$SignalingState");
+  LoadClass(jni, "org/webrtc/RtpReceiver");
+  LoadClass(jni, "org/webrtc/RtpSender");
+  LoadClass(jni, "org/webrtc/SessionDescription");
+  LoadClass(jni, "org/webrtc/SessionDescription$Type");
+  LoadClass(jni, "org/webrtc/StatsReport");
+  LoadClass(jni, "org/webrtc/StatsReport$Value");
+  LoadClass(jni, "org/webrtc/SurfaceTextureHelper");
+  LoadClass(jni, "org/webrtc/VideoCapturer");
+  LoadClass(jni, "org/webrtc/VideoCapturer$NativeObserver");
+  LoadClass(jni, "org/webrtc/VideoRenderer$I420Frame");
+  LoadClass(jni, "org/webrtc/VideoTrack");
+}
+
+ClassReferenceHolder::~ClassReferenceHolder() {
+  RTC_CHECK(classes_.empty()) << "Must call FreeReferences() before dtor!";
+}
+
+void ClassReferenceHolder::FreeReferences(JNIEnv* jni) {
+  for (std::map<std::string, jclass>::const_iterator it = classes_.begin();
+      it != classes_.end(); ++it) {
+    jni->DeleteGlobalRef(it->second);
+  }
+  classes_.clear();
+}
+
+jclass ClassReferenceHolder::GetClass(const std::string& name) {
+  std::map<std::string, jclass>::iterator it = classes_.find(name);
+  RTC_CHECK(it != classes_.end()) << "Unexpected GetClass() call for: " << name;
+  return it->second;
+}
+
+void ClassReferenceHolder::LoadClass(JNIEnv* jni, const std::string& name) {
+  jclass localRef = jni->FindClass(name.c_str());
+  CHECK_EXCEPTION(jni) << "error during FindClass: " << name;
+  RTC_CHECK(localRef) << name;
+  jclass globalRef = reinterpret_cast<jclass>(jni->NewGlobalRef(localRef));
+  CHECK_EXCEPTION(jni) << "error during NewGlobalRef: " << name;
+  RTC_CHECK(globalRef) << name;
+  bool inserted = classes_.insert(std::make_pair(name, globalRef)).second;
+  RTC_CHECK(inserted) << "Duplicate class name: " << name;
+}
+
+// Returns a global reference guaranteed to be valid for the lifetime of the
+// process.
+jclass FindClass(JNIEnv* jni, const char* name) {
+  return g_class_reference_holder->GetClass(name);
+}
+
+}  // namespace webrtc_jni