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

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

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights
  * reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
@@ skipping 414 matching lines @@
 void PaintLayer::updateTransform(const ComputedStyle* oldStyle,
                                  const ComputedStyle& newStyle) {
   if (oldStyle && newStyle.transformDataEquivalent(*oldStyle))
     return;
 
   // hasTransform() on the layoutObject is also true when there is
   // transform-style: preserve-3d or perspective set, so check style too.
   bool hasTransform =
       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)
       ensureRareData().transform = TransformationMatrix::create();
     else
       m_rareData->transform.reset();
 
     // PaintLayers with transforms act as clip rects roots, so clear the cached
     // clip rects here.
     clipper().clearClipRectsIncludingDescendants();
@@ skipping 2843 matching lines @@
 }
 
 void showLayerTree(const blink::LayoutObject* layoutObject) {
   if (!layoutObject) {
     LOG(INFO) << "Cannot showLayerTree. Root is (nil)";
     return;
   }
   showLayerTree(layoutObject->enclosingLayer());
 }
 #endif