Make ViewportScrollCallback an interface and add child and root classes

third_party/WebKit/Source/core/page/scrolling/RootViewportScrollCallback.cpp

Index: third_party/WebKit/Source/core/page/scrolling/RootViewportScrollCallback.cpp
diff --git a/third_party/WebKit/Source/core/page/scrolling/ViewportScrollCallback.cpp b/third_party/WebKit/Source/core/page/scrolling/RootViewportScrollCallback.cpp
similarity index 58%
copy from third_party/WebKit/Source/core/page/scrolling/ViewportScrollCallback.cpp
copy to third_party/WebKit/Source/core/page/scrolling/RootViewportScrollCallback.cpp
index f8cc13a7ff8d3c9b0a824568832561bc51bfe749..a75ebc3a0c280ad08012e8461212c700d4233ec3 100644
--- a/third_party/WebKit/Source/core/page/scrolling/ViewportScrollCallback.cpp
+++ b/third_party/WebKit/Source/core/page/scrolling/RootViewportScrollCallback.cpp
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "core/page/scrolling/ViewportScrollCallback.h"
+#include "core/page/scrolling/RootViewportScrollCallback.h"
 
 #include "core/frame/FrameHost.h"
 #include "core/frame/FrameView.h"
@@ -15,26 +15,26 @@
 
 namespace blink {
 
-ViewportScrollCallback::ViewportScrollCallback(
+RootViewportScrollCallback::RootViewportScrollCallback(
     TopControls* topControls, OverscrollController* overscrollController)
     : m_topControls(topControls)
     , m_overscrollController(overscrollController)
 {
 }
 
-ViewportScrollCallback::~ViewportScrollCallback()
+RootViewportScrollCallback::~RootViewportScrollCallback()
 {
 }
 
-DEFINE_TRACE(ViewportScrollCallback)
+DEFINE_TRACE(RootViewportScrollCallback)
 {
     visitor->trace(m_topControls);
     visitor->trace(m_overscrollController);
     visitor->trace(m_scroller);
-    ScrollStateCallback::trace(visitor);
+    ViewportScrollCallback::trace(visitor);
 }
 
-bool ViewportScrollCallback::shouldScrollTopControls(const FloatSize& delta,
+bool RootViewportScrollCallback::shouldScrollTopControls(const FloatSize& delta,
     ScrollGranularity granularity) const
 {
     if (granularity != ScrollByPixel && granularity != ScrollByPrecisePixel)
@@ -53,32 +53,39 @@ bool ViewportScrollCallback::shouldScrollTopControls(const FloatSize& delta,
     return delta.height() < 0 || scrollPosition.y() < maxScroll.y();
 }
 
-void ViewportScrollCallback::handleEvent(ScrollState* state)
+bool RootViewportScrollCallback::scrollTopControls(ScrollState& state)
 {
-    FloatSize delta(state->deltaX(), state->deltaY());
-    ScrollGranularity granularity =
-        ScrollGranularity(static_cast<int>(state->deltaGranularity()));
-    FloatSize remainingDelta = delta;
-
     // Scroll top controls.
     if (m_topControls) {
-        if (state->isBeginning())
+        if (state.isBeginning())
             m_topControls->scrollBegin();
 
-        if (shouldScrollTopControls(delta, granularity))
-            remainingDelta = m_topControls->scrollBy(delta);
+        FloatSize delta(state.deltaX(), state.deltaY());
+        ScrollGranularity granularity =
+            ScrollGranularity(static_cast<int>(state.deltaGranularity()));
+        if (shouldScrollTopControls(delta, granularity)) {
+            FloatSize remainingDelta = m_topControls->scrollBy(delta);
+            FloatSize consumed = delta - remainingDelta;
+            state.consumeDeltaNative(consumed.width(), consumed.height());
+            return !consumed.isZero();
+        }
     }
 
-    bool topControlsConsumedScroll = remainingDelta.height() != delta.height();
+    return false;
+}
 
-    // Scroll the element's scrollable area.
+void RootViewportScrollCallback::handleEvent(ScrollState* state)
+{
+    DCHECK(state);
     if (!m_scroller)
         return;
 
-    ScrollResult result = m_scroller->userScroll(granularity, remainingDelta);
+    bool topControlsDidScroll = scrollTopControls(*state);
+
+    ScrollResult result = performNativeScroll(*state, *m_scroller);
 
     // We consider top controls movement to be scrolling.
-    result.didScrollY |= topControlsConsumedScroll;
+    result.didScrollY |= topControlsDidScroll;
 
     // Handle Overscroll.
     if (m_overscrollController) {
@@ -86,17 +93,9 @@ void ViewportScrollCallback::handleEvent(ScrollState* state)
         FloatSize velocity(state->velocityX(), state->velocityY());
         m_overscrollController->handleOverscroll(result, position, velocity);
     }
-
-    // The viewport consumes everything.
-    // TODO(bokan): This isn't actually consuming everything but doing so breaks
-    // the main thread pull-to-refresh action. I need to figure out where that
-    // gets activated. crbug.com/607210.
-    state->consumeDeltaNative(
-        state->deltaX() - result.unusedScrollDeltaX,
-        state->deltaY() - result.unusedScrollDeltaY);
 }
 
-void ViewportScrollCallback::setScroller(ScrollableArea* scroller)
+void RootViewportScrollCallback::setScroller(ScrollableArea* scroller)
 {
     m_scroller = scroller;
 }