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 d4ad116c39304c12eca8c2894220897269aa7b20..b0a9d7edf5acefdc6eba5d53fc1467e43c426ced 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"
@@ -334,6 +335,18 @@ bool VTVideoDecodeAccelerator::ConfigureDecoder() {
     return false;
   }
 
+  // Report whether hardware decode is being used.
+  base::ScopedCFTypeRef<CFBooleanRef> using_hardware;
+  if (VTSessionCopyProperty(
+          session_,
+          // kVTDecompressionPropertyKey_UsingHardwareAcceleratedVideoDecoder
+          CFSTR("UsingHardwareAcceleratedVideoDecoder"),
+          kCFAllocatorDefault,
+          using_hardware.InitializeInto()) == 0) {
+    UMA_HISTOGRAM_BOOLEAN("Media.VTVDA.HardwareAccelerated",
+                          CFBooleanGetValue(using_hardware));
+  }
+
   return true;
 }