Add flag to beginRecording to request saveLayer information

cc/resources/gpu_raster_worker_pool.cc

Index: cc/resources/gpu_raster_worker_pool.cc
diff --git a/cc/resources/gpu_raster_worker_pool.cc b/cc/resources/gpu_raster_worker_pool.cc
index c9139706f81bf9620bc90536936ac7061dabf041..c6f9ea110db5f3b93062a92480573f85d183e59b 100644
--- a/cc/resources/gpu_raster_worker_pool.cc
+++ b/cc/resources/gpu_raster_worker_pool.cc
@@ -48,8 +48,11 @@ class RasterBufferImpl : public RasterBuffer {
 
     SkPictureRecorder recorder;
     gfx::Size size = resource_->size();
+    const int flags = SkPictureRecorder::kComputeSaveLayerInfo_RecordFlag;
     skia::RefPtr<SkCanvas> canvas =
-        skia::SharePtr(recorder.beginRecording(size.width(), size.height()));
+        skia::SharePtr(recorder.beginRecording(size.width(), size.height(),
+                                               NULL, flags));
+
 
     canvas->save();
     raster_source->PlaybackToCanvas(canvas.get(), rect, scale);