Adds method to provide custom AudioManager at runtime.

media/audio/audio_manager.cc

Index: media/audio/audio_manager.cc
diff --git a/media/audio/audio_manager.cc b/media/audio/audio_manager.cc
index 6ee61d16cd7bd6ad3beb3a2cf912b7f4ac1aeffe..4cb3278e6297fe519e282f0b0172a6ce7952e0dd 100644
--- a/media/audio/audio_manager.cc
+++ b/media/audio/audio_manager.cc
@@ -12,12 +12,22 @@
 #include "base/message_loop/message_loop.h"
 #include "base/power_monitor/power_monitor.h"
 #include "build/build_config.h"
+#include "media/audio/audio_manager_factory.h"
 #include "media/audio/fake_audio_log_factory.h"
 
 namespace media {
 namespace {
+
+// The singleton instance of AudioManager. This is set when Create() is called.
 AudioManager* g_last_created = NULL;
 
+// The singleton instance of AudioManagerFactory. This is only set if
+// SetFactory() is called. If it is set when Create() is called, its
+// CreateInstance() function is used to set |g_last_created|. Otherwise, the
+// linked implementation of media::CreateAudioManager is used to set
+// |g_last_created|.
+AudioManagerFactory* g_audio_manager_factory = NULL;
+
 // Maximum number of failed pings to the audio thread allowed. A crash will be
 // issued once this count is reached.  We require at least two pings before
 // crashing to ensure unobservable power events aren't mistakenly caught (e.g.,
@@ -123,7 +133,7 @@ class AudioManagerHelper : public base::PowerObserver {
 
 static base::LazyInstance<AudioManagerHelper>::Leaky g_helper =
     LAZY_INSTANCE_INITIALIZER;
-}
+}  // namespace
 
 // Forward declaration of the platform specific AudioManager factory function.
 AudioManager* CreateAudioManager(AudioLogFactory* audio_log_factory);
@@ -136,9 +146,29 @@ AudioManager::~AudioManager() {
 }
 
 // static
+void AudioManager::SetFactory(AudioManagerFactory* factory) {
+  CHECK(factory);
+  CHECK(!g_last_created);
+  CHECK(!g_audio_manager_factory);
+  g_audio_manager_factory = factory;
+}
+
+// static
+void AudioManager::ResetFactoryForTesting() {
+  if (g_audio_manager_factory) {
+    delete g_audio_manager_factory;
+    g_audio_manager_factory = nullptr;
+  }
+}
+
+// static
 AudioManager* AudioManager::Create(AudioLogFactory* audio_log_factory) {
   CHECK(!g_last_created);
-  g_last_created = CreateAudioManager(audio_log_factory);
+  if (g_audio_manager_factory)
+    g_last_created = g_audio_manager_factory->CreateInstance(audio_log_factory);
+  else
+    g_last_created = CreateAudioManager(audio_log_factory);
+
   return g_last_created;
 }