Disable partial swaps for webview guest renderer until we can figure out how to do that properly.

content/public/common/renderer_preferences.h

Index: content/public/common/renderer_preferences.h
diff --git a/content/public/common/renderer_preferences.h b/content/public/common/renderer_preferences.h
index 4c6ac58887698c73ba112791eaa309c75c64da58..53a6f86891d4852dc42451a87b7483e44b95f0fd 100644
--- a/content/public/common/renderer_preferences.h
+++ b/content/public/common/renderer_preferences.h
@@ -121,6 +121,11 @@ struct CONTENT_EXPORT RendererPreferences {
   // information.
   bool report_frame_name_changes;
 
+  // Specifies whether partially swapping composited buffers is
+  // allowed for a renderer. Partial swaps will be used if they are both
+  // allowed and supported.
+  bool allow_partial_swap;
+
   // Controls deacceleration of touchpad-initiated flings.
   std::vector<float> touchpad_fling_profile;