Add UMA metrics to OffscreenCanvas's commit type

third_party/WebKit/Source/platform/graphics/OffscreenCanvasFrameDispatcherImpl.h

Index: third_party/WebKit/Source/platform/graphics/OffscreenCanvasFrameDispatcherImpl.h
diff --git a/third_party/WebKit/Source/platform/graphics/OffscreenCanvasFrameDispatcherImpl.h b/third_party/WebKit/Source/platform/graphics/OffscreenCanvasFrameDispatcherImpl.h
index 59111dff6b65f56d889e104dd6c59ee6de8c7f77..c38554adc2689fe33bc0d598707a55725c59e961 100644
--- a/third_party/WebKit/Source/platform/graphics/OffscreenCanvasFrameDispatcherImpl.h
+++ b/third_party/WebKit/Source/platform/graphics/OffscreenCanvasFrameDispatcherImpl.h
@@ -37,6 +37,15 @@ class PLATFORM_EXPORT OffscreenCanvasFrameDispatcherImpl final
   void ReturnResources(
       Vector<cc::mojom::blink::ReturnedResourcePtr> resources) override;
 
+  // This enum is used in histogram, so it should be append-only.
+  enum OffscreenCanvasCommitType {
+    CommitGPUCanvasGPUCompositing = 0,
+    CommitGPUCanvasSoftwareCompositing = 1,
+    CommitSoftwareCanvasGPUCompositing = 2,
+    CommitSoftwareCanvasSoftwareCompositing = 3,
+    OffscreenCanvasCommitTypeCount,
+  };
+
  private:
   const cc::SurfaceId m_surfaceId;
   const int m_width;