Fix touch event flag may not be updated correctly by transform which causes no layout

third_party/WebKit/Source/core/paint/PaintLayer.cpp

Index: third_party/WebKit/Source/core/paint/PaintLayer.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayer.cpp b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
index 4f39b06088c6dcdf14872d18b80e9ab4d8baa891..3abc405d0f5ba27ba1906280cb0a0fab4de5a99e 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
@@ -433,6 +433,14 @@ void PaintLayer::updateTransform(const ComputedStyle* oldStyle,
       layoutObject()->hasTransformRelatedProperty() && newStyle.hasTransform();
   bool had3DTransform = has3DTransform();
 

[majidvp, 2017/01/02 21:01:11]

Invalidating touch regions on every transform change for every node feels like
using a BIG hammer. 

Is it possible to limit doing this only for certain transform changes e.g.,
perhaps only when the element actually has a 'touchstart' handler?

[yigu, 2017/01/03 21:21:35]

Done.

+  // When transform does not cause a layout, notifyGeometryChanged()
+  // should be called to correctly update the touch event flags

[majidvp, 2017/01/02 21:01:11]

The comment seems superfluous. It is also a bit incorrect because the logic is
calling notifyGeometryChanged() regardless of whether we need
a layout or not. I think you should just remove the comment.

[yigu, 2017/01/03 21:21:35]

Done.

+  if (hasTransform) {

[majidvp, 2017/01/02 21:01:10]

hmmm, I think this check here is incorrect. You want to recompute
on transform change whether it is adding a transform or removing one.

In fact, why don't you add a test case where removing the transform causes the
touch target to be recomputed.

[yigu, 2017/01/03 21:21:35]

Done.

+    if (ScrollingCoordinator* scrollingCoordinator =
+            layoutObject()->frame()->page()->scrollingCoordinator())
+      scrollingCoordinator->notifyGeometryChanged();

[majidvp, 2017/01/02 21:01:10]

|notifyGeometryChanged| causes recomputation of not only touch regions but also
slow scroll regions. Is this what you wanted?

[yigu, 2017/01/03 21:21:35]

Done.

+  }
+

[majidvp, 2017/01/02 21:01:10]

I rather move this logic at the bottom of the function once transform update
is complete i.e., next to where we notify FrameView of geometry changes.

[yigu, 2017/01/03 21:21:35]

Done.

   bool hadTransform = transform();
   if (hasTransform != hadTransform) {
     if (hasTransform)