Add UMA to track software fallback in VTVideoDecodeAccelerator.

content/common/gpu/media/vt_stubs_header.fragment

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <CoreFoundation/CoreFoundation.h>
 
 extern "C" {
 
 //
 // Declare CoreMedia types.
@@ skipping 48 matching lines @@
 typedef CVBufferRef CVImageBufferRef;
 typedef uint32_t VTDecodeFrameFlags;
 enum {
   kVTDecodeFrame_EnableAsynchronousDecompression = 1 << 0,
   kVTDecodeFrame_DoNotOutputFrame = 1 << 1,
   kVTDecodeFrame_1xRealTimePlayback = 1 << 2,
   kVTDecodeFrame_EnableTemporalProcessing = 1 << 3,
 };
 typedef UInt32 VTDecodeInfoFlags;
 typedef struct OpaqueVTDecompressionSession* VTDecompressionSessionRef;
+typedef CFTypeRef VTSessionRef;
 
 typedef void (*VTDecompressionOutputCallback)(
     void *decompressionOutputRefCon,
     void *sourceFrameRefCon,
     OSStatus status,
     VTDecodeInfoFlags infoFlags,
     CVImageBufferRef imageBuffer,
     CMTime presentationTimeStamp,
     CMTime presentationDuration);
 
 typedef struct {
   VTDecompressionOutputCallback decompressionOutputCallback;
   void *decompressionOutputRefCon;
 } VTDecompressionOutputCallbackRecord;
 
 }  // extern "C"