Add UMA to track software fallback in VTVideoDecodeAccelerator.

content/common/gpu/media/vt_video_decode_accelerator.cc

Index: content/common/gpu/media/vt_video_decode_accelerator.cc
diff --git a/content/common/gpu/media/vt_video_decode_accelerator.cc b/content/common/gpu/media/vt_video_decode_accelerator.cc
index 9a91c9c0f1400ac5f61045a74f3dc5309f7e8164..1de1ce1c3a741f7708d7daf0ee5599e874810af4 100644
--- a/content/common/gpu/media/vt_video_decode_accelerator.cc
+++ b/content/common/gpu/media/vt_video_decode_accelerator.cc
@@ -12,6 +12,7 @@
 #include "base/command_line.h"
 #include "base/logging.h"
 #include "base/mac/mac_logging.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/sys_byteorder.h"
 #include "base/thread_task_runner_handle.h"
 #include "content/common/gpu/media/vt_video_decode_accelerator.h"
@@ -332,6 +333,18 @@ bool VTVideoDecodeAccelerator::ConfigureDecoder() {
     return false;
   }
 
+  // Report whether hardware decode is being used.
+  base::ScopedCFTypeRef<CFBooleanRef> using_hardware;
+  if (VTSessionCopyProperty(

[DaleCurtis, 2014/12/02 18:20:22]

Does clang-format bless this alignment? It looks off.

[sandersd (OOO until July 31), 2014/12/02 18:28:28]

Done.

+        session_,
+        // kVTDecompressionPropertyKey_UsingHardwareAcceleratedVideoDecoder
+        CFSTR("UsingHardwareAcceleratedVideoDecoder"),
+        kCFAllocatorDefault,
+        using_hardware.InitializeInto()) == 0) {
+    UMA_HISTOGRAM_BOOLEAN("Media.VTVDA.UsingHardware",

[DaleCurtis, 2014/12/02 18:20:22]

Don't you need to log this for some of the other failures above? Probably not
the session reinitialization ones, but the others may cause early abort which
falls back to the software path.

[sandersd (OOO until July 31), 2014/12/02 18:28:29]

This is the only path with internal software fallback, if it fails before this
the whole VDA fails.

[DaleCurtis, 2014/12/02 18:29:59]

Ahhhh, as posciak@ noted, you definitely need a better CL description then :) I
thought this was tracking global software fallback.

+                          CFBooleanGetValue(using_hardware));
+  }
+
   return true;
 }