Revert of Removing #defines previously used for building without BoringSSL/OpenSSL. (patchset #2 id:20001 of https://codereview.webrtc.org/2640513002/ )

Reason for revert:
Broke chromium build, due to a config being removed. Will add it back and remove the dependency in a chromium CL.

Original issue's description:
> Removing #defines previously used for building without BoringSSL/OpenSSL.
>
> These defines don't work any more, so they only cause confusion:
>
> FEATURE_ENABLE_SSL
> HAVE_OPENSSL_SSL_H
> SSL_USE_OPENSSL
>
> BUG=webrtc:7025
>
> Review-Url: https://codereview.webrtc.org/2640513002
> Cr-Commit-Position: refs/heads/master@{#16196}
> Committed: https://chromium.googlesource.com/external/webrtc/+/eaa826c2ee0668cfb4a0dfb66f8d388b65da20f5

TBR=kjellander@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=webrtc:7025

Review-Url: https://codereview.webrtc.org/2648003003
Cr-Commit-Position: refs/heads/master@{#16197}
diff --git a/webrtc/base/opensslstreamadapter.cc b/webrtc/base/opensslstreamadapter.cc
index 158315f..3b3aa5d 100644
--- a/webrtc/base/opensslstreamadapter.cc
+++ b/webrtc/base/opensslstreamadapter.cc
@@ -8,6 +8,8 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
+#if HAVE_OPENSSL_SSL_H
+
 #include "webrtc/base/opensslstreamadapter.h"
 
 #include <openssl/bio.h>
@@ -43,10 +45,11 @@
 
 namespace rtc {
 
-#if (OPENSSL_VERSION_NUMBER < 0x10001000L)
-#error "webrtc requires at least OpenSSL version 1.0.1, to support DTLS-SRTP"
+#if (OPENSSL_VERSION_NUMBER >= 0x10001000L)
+#define HAVE_DTLS_SRTP
 #endif
 
+#ifdef HAVE_DTLS_SRTP
 // SRTP cipher suite table. |internal_name| is used to construct a
 // colon-separated profile strings which is needed by
 // SSL_CTX_set_tlsext_use_srtp().
@@ -62,6 +65,7 @@
     {"SRTP_AEAD_AES_128_GCM", SRTP_AEAD_AES_128_GCM},
     {"SRTP_AEAD_AES_256_GCM", SRTP_AEAD_AES_256_GCM},
     {nullptr, 0}};
+#endif
 
 #ifdef OPENSSL_IS_BORINGSSL
 // Not used in production code. Actual time should be relative to Jan 1, 1970.
@@ -428,6 +432,7 @@
                                                 bool use_context,
                                                 uint8_t* result,
                                                 size_t result_len) {
+#ifdef HAVE_DTLS_SRTP
   int i;
 
   i = SSL_export_keying_material(ssl_, result, result_len, label.c_str(),
@@ -438,10 +443,14 @@
     return false;
 
   return true;
+#else
+  return false;
+#endif
 }
 
 bool OpenSSLStreamAdapter::SetDtlsSrtpCryptoSuites(
     const std::vector<int>& ciphers) {
+#ifdef HAVE_DTLS_SRTP
   std::string internal_ciphers;
 
   if (state_ != SSL_NONE)
@@ -472,9 +481,13 @@
 
   srtp_ciphers_ = internal_ciphers;
   return true;
+#else
+  return false;
+#endif
 }
 
 bool OpenSSLStreamAdapter::GetDtlsSrtpCryptoSuite(int* crypto_suite) {
+#ifdef HAVE_DTLS_SRTP
   RTC_DCHECK(state_ == SSL_CONNECTED);
   if (state_ != SSL_CONNECTED)
     return false;
@@ -488,6 +501,9 @@
   *crypto_suite = srtp_profile->id;
   RTC_DCHECK(!SrtpCryptoSuiteToName(*crypto_suite).empty());
   return true;
+#else
+  return false;
+#endif
 }
 
 bool OpenSSLStreamAdapter::IsTlsConnected() {
@@ -1080,12 +1096,14 @@
   SSL_CTX_set_cipher_list(ctx,
       "DEFAULT:!NULL:!aNULL:!SHA256:!SHA384:!aECDH:!AESGCM+AES256:!aPSK");
 
+#ifdef HAVE_DTLS_SRTP
   if (!srtp_ciphers_.empty()) {
     if (SSL_CTX_set_tlsext_use_srtp(ctx, srtp_ciphers_.c_str())) {
       SSL_CTX_free(ctx);
       return NULL;
     }
   }
+#endif
 
   return ctx;
 }
@@ -1151,6 +1169,26 @@
   return stream->VerifyPeerCertificate();
 }
 
+bool OpenSSLStreamAdapter::HaveDtls() {
+  return true;
+}
+
+bool OpenSSLStreamAdapter::HaveDtlsSrtp() {
+#ifdef HAVE_DTLS_SRTP
+  return true;
+#else
+  return false;
+#endif
+}
+
+bool OpenSSLStreamAdapter::HaveExporter() {
+#ifdef HAVE_DTLS_SRTP
+  return true;
+#else
+  return false;
+#endif
+}
+
 bool OpenSSLStreamAdapter::IsBoringSsl() {
 #ifdef OPENSSL_IS_BORINGSSL
   return true;
@@ -1235,3 +1273,5 @@
 }
 
 }  // namespace rtc
+
+#endif  // HAVE_OPENSSL_SSL_H