Nit

Author: Emmanuel Garcia

flow/embedded_views.h

@@ -249,7 +249,7 @@ class ExternalViewEmbedder {
   // Must be called on the UI thread.
   virtual SkCanvas* CompositeEmbeddedView(int view_id) = 0;
 
-  // Submits the frame by calling frame.Submit().
+  // Implementers must submit the frame by calling frame.Submit().
   //
   // This method can mutate the root Skia canvas before submitting the frame.
   //