Move overscroll logic out of EventHandler.

third_party/WebKit/Source/core/page/scrolling/OverscrollController.h

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef OverscrollController_h
+#define OverscrollController_h
+
+#include "platform/geometry/FloatSize.h"
+#include "platform/heap/Handle.h"
+
+namespace blink {
+
+class ChromeClient;
+class FloatPoint;
+struct ScrollResult;
+class VisualViewport;
+
+// Handles overscroll logic that occurs when the user scolls past the end of the
+// document's scroll extents. Currently, this applies only to document scrolling
+// and only on the root frame. We "accumulate" overscroll deltas from separate
+// scroll events if the user continuously scrolls past the extent but reset it
+// as soon as a gesture ends.
+class OverscrollController : public GarbageCollected<OverscrollController> {
+public:
+    static OverscrollController* create(
+        VisualViewport& visualViewport,
+        ChromeClient& chromeClient) {
+        return new OverscrollController(visualViewport, chromeClient);
+    }
+
+    void resetAccumulated(bool resetX, bool resetY);
+
+    // Reports unused scroll as overscroll to the content layer. The position
+    // argument is the most recent location of the gesture, the finger position
+    // for touch scrolling and the cursor position for wheel. Velocity is used
+    // in the case of a fling gesture where we want the overscroll to feel like
+    // it has momentum.
+    void handleOverscroll(
+        const ScrollResult&,
+        const FloatPoint& positionInRootFrame,
+        const FloatSize& velocityInRootFrame);
+
+    DECLARE_TRACE();
+
+private:
+    OverscrollController(VisualViewport&, ChromeClient&);
+
+    WeakMember<VisualViewport> m_visualViewport;

[bokan, 2016/04/25 13:44:21]

This should really be `const VisualViewport` but WeakMember blows up with a
const type (Memeber works fine). I've sent off a query to oilpan-reviews@ about
this but made it non-const in the mean time.

[bokan, 2016/04/26 01:08:41]

Oilpan team fixed so I made this const again.

+    ChromeClient& m_chromeClient;
+
+    FloatSize m_accumulatedRootOverscroll;
+};
+
+} // namespace blink
+
+#endif // OverscrollController_h