To accommodate some downstream WebRTC users we need to loosen
the coupling between our code and the //third_party/protobuf.

This includes using typedefs to define strings instead of
assuming std::string.

After this refactoring it will be possible to link with other
protobuf implementations than the current one.

We moved the PRESUBMIT check to another CL [1]. The goal of this
presubmit is to avoid the direct usage of google::protobuf outside
of the webrtc/base/protobuf_utils.h header file.

[1] - https://codereview.webrtc.org/2753823003/

BUG=webrtc:7340
NOTRY=True

Review-Url: https://codereview.webrtc.org/2747863003
Cr-Commit-Position: refs/heads/master@{#17466}
diff --git a/webrtc/modules/audio_processing/test/protobuf_utils.cc b/webrtc/modules/audio_processing/test/protobuf_utils.cc
index c18a13e..cb8adf9 100644
--- a/webrtc/modules/audio_processing/test/protobuf_utils.cc
+++ b/webrtc/modules/audio_processing/test/protobuf_utils.cc
@@ -30,7 +30,7 @@
 }
 
 // Returns true on success, false on error or end-of-file.
-bool ReadMessageFromFile(FILE* file, ::google::protobuf::MessageLite* msg) {
+bool ReadMessageFromFile(FILE* file, MessageLite* msg) {
   std::unique_ptr<uint8_t[]> bytes;
   size_t size = ReadMessageBytesFromFile(file, &bytes);
   if (!size)