Fix frame coordinate translation issue with scroll views.

third_party/WebKit/Source/web/WebInputEventConversion.cpp

Index: third_party/WebKit/Source/web/WebInputEventConversion.cpp
diff --git a/third_party/WebKit/Source/web/WebInputEventConversion.cpp b/third_party/WebKit/Source/web/WebInputEventConversion.cpp
index 7b9defc7bf238a88ca6681c5367b07a8f38c8403..b7092abc7a0a7448b8ad936dc455bef3ab22314a 100644
--- a/third_party/WebKit/Source/web/WebInputEventConversion.cpp
+++ b/third_party/WebKit/Source/web/WebInputEventConversion.cpp
@@ -196,6 +196,13 @@ WebMouseEventBuilder::WebMouseEventBuilder(const FrameView* plugin_parent,
     *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());