Oilpan: improve ScrollableArea handling.

Source/platform/scroll/ScrollableArea.h

 /*
  * Copyright (C) 2008, 2011 Apple Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 11 matching lines @@
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef ScrollableArea_h
 #define ScrollableArea_h
 
 #include "platform/PlatformExport.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/geometry/DoublePoint.h"
+#include "platform/heap/Handle.h"
 #include "platform/scroll/ScrollAnimator.h"
 #include "platform/scroll/ScrollTypes.h"
 #include "platform/scroll/Scrollbar.h"
 #include "wtf/Noncopyable.h"
 #include "wtf/Vector.h"
 
 namespace blink {
 
 class DoubleRect;
 class FloatPoint;
 class GraphicsLayer;
 class HostWindow;
 class PlatformWheelEvent;
 class ProgrammaticScrollAnimator;
 struct ScrollAlignment;
 class ScrollAnimator;
 
 enum ScrollBehavior {
     ScrollBehaviorAuto,
     ScrollBehaviorInstant,
     ScrollBehaviorSmooth,
 };
 
 enum IncludeScrollbarsInRect {
     ExcludeScrollbars,
     IncludeScrollbars,
 };
 
+#if ENABLE(OILPAN)
+// Oilpan: Using the transition type WillBeGarbageCollectedMixin is
+// problematic non-Oilpan as the type expands to DummyBase, exporting it
+// also from 'platform' as a result. Bringing about duplicate DummyBases
+// as core also exports same; with component build linking fails as a
+// result. Hence the workaround of not using a transition type.
+class PLATFORM_EXPORT ScrollableArea : public GarbageCollectedMixin {
+#else
 class PLATFORM_EXPORT ScrollableArea {
+#endif
     WTF_MAKE_NONCOPYABLE(ScrollableArea);
 public:
     static int pixelsPerLineStep();
     static float minFractionToStepWhenPaging();
     static int maxOverlapBetweenPages();
 
     // Convert a non-finite scroll value (Infinity, -Infinity, NaN) to 0 as
     // per http://dev.w3.org/csswg/cssom-view/#normalize-non_finite-values.
     static double normalizeNonFiniteScroll(double value) { return std::isfinite(value) ? value : 0.0; }
 
@@ skipping 211 matching lines @@
     // TODO(bokan): FrameView::setScrollPosition uses updateScrollbars to scroll
     // which bails out early if its already in updateScrollbars, the effect being
     // that programmatic scrolls (i.e. setScrollPosition) are disabled when in
     // updateScrollbars. Expose this here to allow RootFrameViewport to match the
     // semantics for now but it should be cleaned up at the source.
     virtual bool isProgrammaticallyScrollable() { return true; }
 
     // Subtracts space occupied by this ScrollableArea's scrollbars.
     // Does nothing if overlay scrollbars are enabled.
     IntSize excludeScrollbars(const IntSize&) const;
+
+    // Need to promptly let go of owned animator objects.

[haraken, 2015/06/29 15:20:22]

I don't fully understand this -- why do we need to promptly destruct
ScrollAnimator?

[sof, 2015/06/29 15:59:41]

Look at ScrollAnimatorMac and the back references it keeps to ScrollableArea.
And timers, which make them susceptible to lazy sweeping instability.

+    EAGERLY_FINALIZE();
+    DEFINE_INLINE_VIRTUAL_TRACE() { }
+
 protected:
     ScrollableArea();
 
     void setScrollOrigin(const IntPoint&);
     void resetScrollOriginChanged() { m_scrollOriginChanged = false; }
 
     // Needed to let the animators call scrollPositionChanged.
     friend class ScrollAnimator;
     friend class ProgrammaticScrollAnimator;
     void scrollPositionChanged(const DoublePoint&, ScrollType);
@@ skipping 18 matching lines @@
     virtual int lineStep(ScrollbarOrientation) const;
     virtual int pageStep(ScrollbarOrientation) const;
     virtual int documentStep(ScrollbarOrientation) const;
     virtual float pixelStep(ScrollbarOrientation) const;
 
     // Stores the paint invalidations for the scrollbars during layout.
     IntRect m_horizontalBarDamage;
     IntRect m_verticalBarDamage;
 
     struct ScrollableAreaAnimators {
-        RefPtr<ScrollAnimator> scrollAnimator;
+        OwnPtr<ScrollAnimator> scrollAnimator;
         OwnPtr<ProgrammaticScrollAnimator> programmaticScrollAnimator;
     };
 
     mutable OwnPtr<ScrollableAreaAnimators> m_animators;
 
     unsigned m_inLiveResize : 1;
 
     unsigned m_scrollbarOverlayStyle : 2; // ScrollbarOverlayStyle
 
     unsigned m_scrollOriginChanged : 1;
 
     // There are 8 possible combinations of writing mode and direction. Scroll origin will be non-zero in the x or y axis
     // if there is any reversed direction or writing-mode. The combinations are:
     // writing-mode / direction     scrollOrigin.x() set    scrollOrigin.y() set
     // horizontal-tb / ltr          NO                      NO
     // horizontal-tb / rtl          YES                     NO
     // horizontal-bt / ltr          NO                      YES
     // horizontal-bt / rtl          YES                     YES
     // vertical-lr / ltr            NO                      NO
     // vertical-lr / rtl            NO                      YES
     // vertical-rl / ltr            YES                     NO
     // vertical-rl / rtl            YES                     YES
     IntPoint m_scrollOrigin;
 };
 
 } // namespace blink
 
 #endif // ScrollableArea_h