Fix frame coordinate translation issue with scroll views.

third_party/WebKit/Source/web/WebInputEventConversion.cpp

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 177 matching lines @@
   return TransformWebTouchEvent(FrameScale(frame_view),
                                 FrameTranslation(frame_view), event);
 }
 
 WebMouseEventBuilder::WebMouseEventBuilder(const FrameView* plugin_parent,
                                            const LayoutItem layout_item,
                                            const MouseEvent& event) {
   if (event.NativeEvent()) {
     *static_cast<WebMouseEvent*>(this) =
         event.NativeEvent()->FlattenTransform();
     WebFloatPoint absolute_root_frame_location = PositionInRootFrame();

[mustaq, 2017/04/12 15:38:38]

Nit: after flattening, s/PositionInRootFrame()/PositionInWidget()/ is better?

[bokan, 2017/04/12 17:28:44]

Isn't the transform what gets us from Widget to RootFrame? i.e. the pinch scale
and pan. In which case it's currently correct...

[mustaq, 2017/04/12 17:52:04]

|PositionInRootFrame| is correct but I thought |PositionInWidget| is a faster
way to get the same coordinates after the FlattenTransform() above (which makes
the transform stored in |*this| is a no-op)---if I am not missing something else
in between.

[dtapuska, 2017/04/12 19:02:56]

Ya it is the same. But for readability sake we probably should keep it with the
slower version.

+
+    // Translate the root frame position to content coordinates.
+    if (plugin_parent) {

[bokan, 2017/04/12 17:28:44]

There seems to be only one call site and plugin_parent should never be null.
Could you add a TODO to remove the if (better not to do here since we're
merging). Also, change absolute_root_frame_location -> absolute_location or
content_location.

[dtapuska, 2017/04/12 19:02:56]

Done.

+      absolute_root_frame_location =
+          plugin_parent->RootFrameToContents(absolute_root_frame_location);
+    }
+
     IntPoint local_point = RoundedIntPoint(layout_item.AbsoluteToLocal(
         absolute_root_frame_location, kUseTransforms));
     SetPositionInWidget(local_point.X(), local_point.Y());
     return;
   }
 
   // Code below here can be removed once OOPIF ships.
   // OOPIF will prevent synthetic events being dispatched into
   // other frames; but for now we allow the fallback to generate
   // WebMouseEvents from synthetic events.
@@ skipping 163 matching lines @@
   Vector<WebTouchEvent> result;
   for (const auto& event : coalesced_events) {
     DCHECK(WebInputEvent::IsTouchEventType(event->GetType()));
     result.push_back(TransformWebTouchEvent(
         scale, translation, static_cast<const WebTouchEvent&>(*event)));
   }
   return result;
 }
 
 }  // namespace blink