Expose locks for CopyFromCompositingSurface/CopyFromBackingStore API

content/port/browser/render_widget_host_view_port.h

Index: content/port/browser/render_widget_host_view_port.h
diff --git a/content/port/browser/render_widget_host_view_port.h b/content/port/browser/render_widget_host_view_port.h
index aa2b21828ddf88b2add1201d5ec469a75680f499..bb07f836bfcc94fd9b785dc4872b73932044bde5 100644
--- a/content/port/browser/render_widget_host_view_port.h
+++ b/content/port/browser/render_widget_host_view_port.h
@@ -189,6 +189,10 @@ class CONTENT_EXPORT RenderWidgetHostViewPort : public RenderWidgetHostView,
       const base::Callback<void(bool, const SkBitmap&)>& callback,
       const SkBitmap::Config config) = 0;
 
+  // Instructs the view to not drop the surface even when the view is hidden.
+  virtual void LockCompositingSurface() = 0;
+  virtual void UnlockCompositingSurface() = 0;
+
   // Copies a given subset of the compositing surface's content into a YV12
   // VideoFrame, and invokes a callback with a success/fail parameter. |target|
   // must contain an allocated, YV12 video frame of the intended size. If the