Re-enable ScrollbarAnimationController::DidRequestShowFromMainThread.

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>
@@ skipping 526 matching lines @@
   }
 
   // TODO(szager): Handle fractional scroll offsets correctly.
   return IntRect(
       FlooredIntPoint(ScrollPosition()),
       IntSize(max(0, Layer()->size().Width() - vertical_scrollbar_width),
               max(0, Layer()->size().Height() - horizontal_scrollbar_height)));
 }
 
 void PaintLayerScrollableArea::VisibleSizeChanged() {
+// TODO(skobes): For reasons not fully understood, showing scrollbars from
+// main on viewport size changes regresses memory and perf tests on Android
+// (crbug.com/706927, crbug.com/712453).
+#if !OS(ANDROID)
   ShowOverlayScrollbars();
+#endif
 }
 
 int PaintLayerScrollableArea::VisibleHeight() const {
   return Layer()->size().Height();
 }
 
 int PaintLayerScrollableArea::VisibleWidth() const {
   return Layer()->size().Width();
 }
 
@@ skipping 1565 matching lines @@
 
 void PaintLayerScrollableArea::DelayScrollOffsetClampScope::
     ClampScrollableAreas() {
   for (auto& scrollable_area : *needs_clamp_)
     scrollable_area->ClampScrollOffsetAfterOverflowChange();
   delete needs_clamp_;
   needs_clamp_ = nullptr;
 }
 
 }  // namespace blink