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/audio_processing_impl.cc b/webrtc/modules/audio_processing/audio_processing_impl.cc
index 1f73c59..56da282 100644
--- a/webrtc/modules/audio_processing/audio_processing_impl.cc
+++ b/webrtc/modules/audio_processing/audio_processing_impl.cc
@@ -1879,11 +1879,11 @@
   audioproc::Init* msg = debug_dump_.capture.event_msg->mutable_init();
   msg->set_sample_rate(formats_.api_format.input_stream().sample_rate_hz());
 
-  msg->set_num_input_channels(static_cast<google::protobuf::int32>(
+  msg->set_num_input_channels(static_cast<int32_t>(
       formats_.api_format.input_stream().num_channels()));
-  msg->set_num_output_channels(static_cast<google::protobuf::int32>(
+  msg->set_num_output_channels(static_cast<int32_t>(
       formats_.api_format.output_stream().num_channels()));
-  msg->set_num_reverse_channels(static_cast<google::protobuf::int32>(
+  msg->set_num_reverse_channels(static_cast<int32_t>(
       formats_.api_format.reverse_input_stream().num_channels()));
   msg->set_reverse_sample_rate(
       formats_.api_format.reverse_input_stream().sample_rate_hz());
@@ -1953,7 +1953,7 @@
   }
   config.set_experiments_description(experiments_description);
 
-  std::string serialized_config = config.SerializeAsString();
+  ProtoString serialized_config = config.SerializeAsString();
   if (!forced &&
       debug_dump_.capture.last_serialized_config == serialized_config) {
     return kNoError;