cc: Add UMA for tracking decode duration for out of raster decodes.

cc/tiles/image_decode_cache.h

Index: cc/tiles/image_decode_cache.h
diff --git a/cc/tiles/image_decode_cache.h b/cc/tiles/image_decode_cache.h
index 1b550a6b06e411718ea04d79d05d4cd6f351251d..5415025791564efa03062bd9263fdc76c6f61ec9 100644
--- a/cc/tiles/image_decode_cache.h
+++ b/cc/tiles/image_decode_cache.h
@@ -6,6 +6,7 @@
 #define CC_TILES_IMAGE_DECODE_CACHE_H_
 
 #include "base/memory/ref_counted.h"
+#include "cc/base/devtools_instrumentation.h"
 #include "cc/paint/draw_image.h"
 #include "cc/tiles/decoded_draw_image.h"
 #include "cc/tiles/tile_priority.h"
@@ -34,22 +35,43 @@ class TileTask;
 //    thread.
 class CC_EXPORT ImageDecodeCache {
  public:
+  enum class TaskType { kInRaster, kOutOfRaster };
+
   // This information should be used strictly in tracing, UMA, and any other
   // reporting systems.
   struct TracingInfo {
     TracingInfo(uint64_t prepare_tiles_id,
-                TilePriority::PriorityBin requesting_tile_bin)
+                TilePriority::PriorityBin requesting_tile_bin,
+                TaskType task_type)
         : prepare_tiles_id(prepare_tiles_id),
-          requesting_tile_bin(requesting_tile_bin) {}
-    TracingInfo() : TracingInfo(0, TilePriority::NOW) {}
+          requesting_tile_bin(requesting_tile_bin),
+          task_type(task_type) {}
+    TracingInfo() : TracingInfo(0, TilePriority::NOW, TaskType::kInRaster) {}

[vmpstr, 2017/06/01 21:40:56]

While here, can you just = default this and put the initializers inline below?
Does that work with const members?

[Khushal, 2017/06/01 23:45:09]

Done.

 
     // ID for the current prepare tiles call.
     const uint64_t prepare_tiles_id;
 
     // The bin of the tile that caused this image to be requested.
     const TilePriority::PriorityBin requesting_tile_bin;
+
+    // Whether the decode is requested as a part of tile rasterization.
+    const TaskType task_type;
   };
 
+  static devtools_instrumentation::ScopedImageDecodeTask::TaskType
+  ToScopedTaskType(TaskType task_type) {
+    using ScopedTaskType =
+        devtools_instrumentation::ScopedImageDecodeTask::TaskType;
+    switch (task_type) {
+      case TaskType::kInRaster:
+        return ScopedTaskType::kInRaster;
+      case TaskType::kOutOfRaster:
+        return ScopedTaskType::kOutOfRaster;
+    }
+    NOTREACHED();
+    return ScopedTaskType::kInRaster;
+  }
+
   virtual ~ImageDecodeCache() {}
 
   // Fill in an TileTask which will decode the given image when run. In