cc: Add traces for identification of raster buffer.

cc/raster/zero_copy_raster_buffer_provider.cc

Index: cc/raster/zero_copy_raster_buffer_provider.cc
diff --git a/cc/raster/zero_copy_raster_buffer_provider.cc b/cc/raster/zero_copy_raster_buffer_provider.cc
index 93e8d7e13f07440d2bb6982b62466a5f0cc436d4..b89b45b96a6b7d99aad10fbf527188258988738a 100644
--- a/cc/raster/zero_copy_raster_buffer_provider.cc
+++ b/cc/raster/zero_copy_raster_buffer_provider.cc
@@ -36,6 +36,7 @@ class RasterBufferImpl : public RasterBuffer {
       uint64_t new_content_id,
       float scale,
       const RasterSource::PlaybackSettings& playback_settings) override {
+    TRACE_EVENT0("cc", "ZeroCopyRasterBuffer::Playback");
     gfx::GpuMemoryBuffer* buffer = lock_.GetGpuMemoryBuffer();
     if (!buffer)
       return;