cc: Add traces for identification of raster buffer.

cc/raster/one_copy_raster_buffer_provider.cc

Index: cc/raster/one_copy_raster_buffer_provider.cc
diff --git a/cc/raster/one_copy_raster_buffer_provider.cc b/cc/raster/one_copy_raster_buffer_provider.cc
index 87f8f026a1eb9fc7f6efeb027e9e3c3f3e9abaa4..f0f95ae9bf1eac8248081d484b29fcf30cfd33c1 100644
--- a/cc/raster/one_copy_raster_buffer_provider.cc
+++ b/cc/raster/one_copy_raster_buffer_provider.cc
@@ -46,6 +46,7 @@ class RasterBufferImpl : public RasterBuffer {
       uint64_t new_content_id,
       float scale,
       const RasterSource::PlaybackSettings& playback_settings) override {
+    TRACE_EVENT0("cc", "OneCopyRasterBuffer::Playback");
     worker_pool_->PlaybackAndCopyOnWorkerThread(
         resource_, &lock_, raster_source, raster_full_rect, raster_dirty_rect,
         scale, playback_settings, previous_content_id_, new_content_id);