Fix paint invalidation and painting for composited-scrolling input elements.

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

Index: third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
index 1c356515a000fbe6f1ef14f2e71e5212e912f078..18efa1b515f20432f4eb909d28356cb962aaf0a3 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
@@ -1470,10 +1470,6 @@ void PaintLayerScrollableArea::updateCompositingLayersAfterScroll()
 
 bool PaintLayerScrollableArea::usesCompositedScrolling() const
 {
-    // Scroll form controls on the main thread so they exhibit correct touch scroll event bubbling
-    if (box().isIntrinsicallyScrollable(VerticalScrollbar) || box().isIntrinsicallyScrollable(HorizontalScrollbar))
-        return false;
-
     // See https://codereview.chromium.org/176633003/ for the tests that fail without this disabler.
     DisableCompositingQueryAsserts disabler;
     return layer()->hasCompositedLayerMapping() && layer()->compositedLayerMapping()->scrollingLayer();
@@ -1481,6 +1477,10 @@ bool PaintLayerScrollableArea::usesCompositedScrolling() const
 
 bool PaintLayerScrollableArea::shouldScrollOnMainThread() const
 {
+    // Scroll form controls on the main thread so they exhibit correct touch scroll event bubbling

[bokan, 2016/08/26 15:38:32]

This comment is backwards now since we return "don't scroll on main thread" but
I think we could just get rid of this condition altogether.

[chrishtr, 2016/08/26 15:42:36]

Done.

+    if (box().isIntrinsicallyScrollable(VerticalScrollbar) || box().isIntrinsicallyScrollable(HorizontalScrollbar))
+        return false;
+
     if (LocalFrame* frame = box().frame()) {
         if (Page* page = frame->page()) {
             if (page->scrollingCoordinator()->shouldUpdateScrollLayerPositionOnMainThread())