Implement top controls show/hide functionality for main thread scrolling

Source/core/frame/TopControls.h

+/*
+ * Copyright (C) 2015 Google 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
+ *     documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
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+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (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 TopControls_h
+#define TopControls_h
+
+#include "platform/heap/Handle.h"
+#include "public/platform/WebTopControlsState.h"
+#include "wtf/OwnPtr.h"
+#include "wtf/PassOwnPtr.h"
+
+namespace blink {
+class FrameHost;
+class FloatSize;
+
+// This class encapsulate data and logic required to scroll top controls.
+// Top controls' self-animation is still handled by compositor and kicks in when
+// scroll is complete (i.e, ScrollEnd, or FlingEnd).

[Rick Byers, 2015/02/19 16:38:38]

nit: Add a comment saying that this duplicates CC's logic in TopControlsManager.

[majidvp, 2015/02/19 19:18:01]

Done.

+class TopControls final : public NoBaseWillBeGarbageCollectedFinalized<TopControls> {
+public:
+    static PassOwnPtrWillBeRawPtr<TopControls> create(const FrameHost& host)
+    {
+        return adoptPtrWillBeNoop(new TopControls(host));
+    }
+
+    // The amount that the viewport was shrunk by to accommodate the top
+    // controls.
+    float layoutHeight();
+    // The amount that top controls are currently shown.
+    float contentOffset();
+
+    float height() const { return m_height; }
+    bool shrinkViewport() const { return m_shrinkViewport; }
+    void setHeight(float height, bool shrinkViewport);
+
+    float shownRatio() const { return m_shownRatio; }
+    void setShownRatio(float);
+
+    void updateConstraints(WebTopControlsState constraints);
+
+    void scrollBegin();
+
+    // Scrolls top controls vertically if possible and returns the remaining scroll
+    // amount.
+    FloatSize scrollBy(FloatSize scrollDelta);

[Rick Byers, 2015/02/19 16:38:38]

conceptually this is a scroll customization (custom 'applyScroll' method on the
root document).  Perhaps once +tdresser lands his scroll customization CLs there
will be an opportunity to decouple this a bit using his new abstraction?

[majidvp, 2015/02/19 19:18:01]

I agree we should be able to model this as yet another custom scroller in the
chain. I looked into having top controls implement ScrollableArea interface but
its abstraction is heavily tied with graphics layer and scrollbars and not
really a good fit for top controls IMO.

+
+private:
+    explicit TopControls(const FrameHost&);
+    void resetBaseline();
+
+    const FrameHost& m_frameHost;
+
+    // The top controls height regardless of whether it is visible or not.
+    // |layoutHeight()| give your the amount that viewport is shrunk to

[Rick Byers, 2015/02/19 16:38:38]

nit: "give your" -> "gives you"?  Although I guess this sentence is entirely
redundant with the comment on layoutHeight.

[majidvp, 2015/02/19 19:18:01]

Removed as it is indeed redundant.

+    // accommodate top controls .
+    float m_height;
+
+    // The top controls shown amount (normalized from 0 to 1) since the last
+    // compositor commit. This value is updated from two sources:
+    // (1) compositor (impl) thread at the beginning of frame if it has
+    //     scrolled top controls since last commit.
+    // (2) blink (main) thread updates this value if it scrolls top controls
+    //     when responding to gesture scroll events.
+    // This value is reflected in web layer tree and is synced with compositor
+    // during the commit.
+    float m_shownRatio;
+
+    // Content offset when last re-baseline occurred.
+    float m_baselineContentOffset;
+
+    // Accumulated scroll delta since last re-baseline.
+    float m_accumulatedScrollDelta;
+
+    // If this is true, then the embedder shrunk the WebView size by the top
+    // controls height.
+    bool m_shrinkViewport;
+
+    // Constraints on the top controls state
+    WebTopControlsState m_permittedState;
+
+};
+} // namespace blink
+
+#endif // TopControls_h