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

third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.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@gmail.com>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 1452 matching lines @@
             layer()->compositedLayerMapping()->setNeedsGraphicsLayerUpdate(GraphicsLayerUpdateSubtree);
             compositor->setNeedsCompositingUpdate(CompositingUpdateAfterGeometryChange);
         } else {
             layer()->setNeedsCompositingInputsUpdate();
         }
     }
 }
 
 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();
 }
 
 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())
                 return true;
         }
     }
     return ScrollableArea::shouldScrollOnMainThread();
 }
 
 static bool layerNeedsCompositedScrolling(PaintLayerScrollableArea::LCDTextMode mode, const PaintLayer* layer)
@@ skipping 279 matching lines @@
 
 void PaintLayerScrollableArea::DelayScrollPositionClampScope::clampScrollableAreas()
 {
     for (auto& scrollableArea : *s_needsClamp)
         scrollableArea->clampScrollPositionsAfterLayout();
     delete s_needsClamp;
     s_needsClamp = nullptr;
 }
 
 } // namespace blink