cc: Add traces for identification of raster buffer.

cc/raster/bitmap_raster_buffer_provider.cc

Index: cc/raster/bitmap_raster_buffer_provider.cc
diff --git a/cc/raster/bitmap_raster_buffer_provider.cc b/cc/raster/bitmap_raster_buffer_provider.cc
index b148860b21e4b16fe1eb8236e6d9a0fe2d2df69d..56e4b573888e58d7a4c6e81f3427ed493bd776af 100644
--- a/cc/raster/bitmap_raster_buffer_provider.cc
+++ b/cc/raster/bitmap_raster_buffer_provider.cc
@@ -42,6 +42,7 @@ class RasterBufferImpl : public RasterBuffer {
       uint64_t new_content_id,
       float scale,
       const RasterSource::PlaybackSettings& playback_settings) override {
+    TRACE_EVENT0("cc", "BitmapRasterBuffer::Playback");
     gfx::Rect playback_rect = raster_full_rect;
     if (resource_has_previous_content_) {
       playback_rect.Intersect(raster_dirty_rect);