Create a private API for controlling WebRTC's AEC3

content/renderer/media/aec_dump_message_filter.h

Index: content/renderer/media/aec_dump_message_filter.h
diff --git a/content/renderer/media/aec_dump_message_filter.h b/content/renderer/media/aec_dump_message_filter.h
index 9cfaf4f1af5887254255a8e255744cbdbfa8ecbd..4bb39cf1eea9a3d856d096db7724882b385c6af9 100644
--- a/content/renderer/media/aec_dump_message_filter.h
+++ b/content/renderer/media/aec_dump_message_filter.h
@@ -21,6 +21,7 @@ namespace content {
 
 // MessageFilter that handles AEC dump messages and forwards them to an
 // observer.
+// TODO(hlundin): Rename class to reflect expanded use; http://crbug.com/709919.
 class CONTENT_EXPORT AecDumpMessageFilter : public IPC::MessageFilter {
  public:
   class AecDumpDelegate {
@@ -28,6 +29,7 @@ class CONTENT_EXPORT AecDumpMessageFilter : public IPC::MessageFilter {
     virtual void OnAecDumpFile(
         const IPC::PlatformFileForTransit& file_handle) = 0;
     virtual void OnDisableAecDump() = 0;
+    virtual void OnAec3Enable(bool enable) = 0;
     virtual void OnIpcClosing() = 0;
   };
 
@@ -73,12 +75,14 @@ class CONTENT_EXPORT AecDumpMessageFilter : public IPC::MessageFilter {
   // Accessed on |io_task_runner_|.
   void OnEnableAecDump(int id, IPC::PlatformFileForTransit file_handle);
   void OnDisableAecDump();
+  void OnEnableAec3(int id, bool enable);
 
   // Accessed on |main_task_runner_|.
   void DoEnableAecDump(int id, IPC::PlatformFileForTransit file_handle);
   void DoDisableAecDump();
   void DoChannelClosingOnDelegates();
   int GetIdForDelegate(AecDumpMessageFilter::AecDumpDelegate* delegate);
+  void DoEnableAec3(int id, bool enable);
 
   // Accessed on |io_task_runner_|.
   IPC::Sender* sender_;
@@ -101,6 +105,12 @@ class CONTENT_EXPORT AecDumpMessageFilter : public IPC::MessageFilter {
   // The singleton instance for this filter.
   static AecDumpMessageFilter* g_filter;
 
+  // When this variable is not set, the use of AEC3 is governed by the Finch
+  // experiment and/or WebRTC's own default. When set to true/false, Finch and
+  // WebRTC defaults will be overridden, and AEC3/AEC2 (respectively) will be
+  // used.
+  base::Optional<bool> override_aec3_;
+
   DISALLOW_COPY_AND_ASSIGN(AecDumpMessageFilter);
 };