Add power monitoring to the Cast VideoToolbox encoder.

media/cast/sender/h264_vt_encoder.cc

Index: media/cast/sender/h264_vt_encoder.cc
diff --git a/media/cast/sender/h264_vt_encoder.cc b/media/cast/sender/h264_vt_encoder.cc
index 346f96fa1d40473e48483238e961014141867153..b5eabeba2756107701182de4dd0642e52f9db8b6 100644
--- a/media/cast/sender/h264_vt_encoder.cc
+++ b/media/cast/sender/h264_vt_encoder.cc
@@ -13,6 +13,7 @@
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/macros.h"
+#include "base/power_monitor/power_monitor.h"
 #include "base/synchronization/lock.h"
 #include "media/base/mac/corevideo_glue.h"
 #include "media/base/mac/video_frame_mac.h"
@@ -333,10 +334,23 @@ H264VideoToolboxEncoder::H264VideoToolboxEncoder(
         scoped_refptr<VideoFrameFactoryImpl>(new VideoFrameFactoryImpl(
             weak_factory_.GetWeakPtr(), cast_environment_));
   }
+
+  // Register for power state changes.
+  auto power_monitor = base::PowerMonitor::Get();
+  if (power_monitor) {
+    power_monitor->AddObserver(this);
+    VLOG(1) << "Registered for power state changes.";
+  } else {
+    DLOG(WARNING) << "No power monitor. Encoder may fail if power state change "
+                     "goes undetected.";
+  }
 }
 
 H264VideoToolboxEncoder::~H264VideoToolboxEncoder() {
   DestroyCompressionSession();
+  auto power_monitor = base::PowerMonitor::Get();
+  if (power_monitor)
+    power_monitor->RemoveObserver(this);
 }
 
 void H264VideoToolboxEncoder::ResetCompressionSession() {
@@ -609,6 +623,18 @@ void H264VideoToolboxEncoder::EmitFrames() {
   }
 }
 
+void H264VideoToolboxEncoder::OnSuspend() {
+  VLOG(1)
+      << "OnSuspend: Emitting all frames and destroying compression session.";
+  EmitFrames();
+  DestroyCompressionSession();
+}
+
+void H264VideoToolboxEncoder::OnResume() {
+  VLOG(1) << "OnResume: Resetting compression session.";
+  ResetCompressionSession();

[miu, 2015/04/22 18:18:47]

I just realized: You shouldn't call ResetCompressionSession() if either:

1. video_frame_factory_ is null (i.e., was never set in the ctor).
2. frame_size_ is empty.

Since these would indicate there wasn't a compression session when OnSuspend()
was called.

[jfroy, 2015/04/22 18:24:36]

Thanks for pointing this out. I'll update the code and make sure to test that
case.

+}
+
 bool H264VideoToolboxEncoder::SetSessionProperty(CFStringRef key,
                                                  int32_t value) {
   base::ScopedCFTypeRef<CFNumberRef> cfvalue(