Roll cc snapshot up to 127605

TBR=nduca@chromium.org
BUG=

Review URL: https://chromiumcodereview.appspot.com/10907075

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@155034 0039d316-1c4b-4281-b951-d872f2087c98

18 files changed, 246 insertions, 67 deletions

diff --git a/cc/CCFrameRateController.cpp b/cc/CCFrameRateController.cpp
index b264bc2..15ff94c 100644
--- a/cc/CCFrameRateController.cpp
+++ b/cc/CCFrameRateController.cpp
@@ -11,6 +11,14 @@
 #include "TraceEvent.h"
 #include <wtf/CurrentTime.h>
 
+namespace {
+
+// This will be the maximum number of pending frames unless
+// CCFrameRateController::setMaxFramesPending is called.
+const int defaultMaxFramesPending = 2;
+
+}
+
 namespace WebCore {
 
 class CCFrameRateControllerTimeSourceAdapter : public CCTimeSourceClient {
@@ -32,9 +40,10 @@ private:
 CCFrameRateController::CCFrameRateController(PassRefPtr<CCTimeSource> timer)
     : m_client(0)
     , m_numFramesPending(0)
-    , m_maxFramesPending(0)
+    , m_maxFramesPending(defaultMaxFramesPending)
     , m_timeSource(timer)
     , m_active(false)
+    , m_swapBuffersCompleteSupported(true)
     , m_isTimeSourceThrottling(true)
 {
     m_timeSourceClientAdapter = CCFrameRateControllerTimeSourceAdapter::create(this);
@@ -44,8 +53,9 @@ CCFrameRateController::CCFrameRateController(PassRefPtr<CCTimeSource> timer)
 CCFrameRateController::CCFrameRateController(CCThread* thread)
     : m_client(0)
     , m_numFramesPending(0)
-    , m_maxFramesPending(0)
+    , m_maxFramesPending(defaultMaxFramesPending)
     , m_active(false)
+    , m_swapBuffersCompleteSupported(true)
     , m_isTimeSourceThrottling(false)
 {
     m_manualTicker = adoptPtr(new CCTimer(thread, this));
@@ -76,6 +86,7 @@ void CCFrameRateController::setActive(bool active)
 
 void CCFrameRateController::setMaxFramesPending(int maxFramesPending)
 {
+    ASSERT(maxFramesPending > 0);
     m_maxFramesPending = maxFramesPending;
 }
 
@@ -85,12 +96,17 @@ void CCFrameRateController::setTimebaseAndInterval(double timebase, double inter
         m_timeSource->setTimebaseAndInterval(timebase, intervalSeconds);
 }
 
+void CCFrameRateController::setSwapBuffersCompleteSupported(bool supported)
+{
+    m_swapBuffersCompleteSupported = supported;
+}
+
 void CCFrameRateController::onTimerTick()
 {
     ASSERT(m_active);
 
     // Don't forward the tick if we have too many frames in flight.
-    if (m_maxFramesPending && m_numFramesPending >= m_maxFramesPending) {
+    if (m_numFramesPending >= m_maxFramesPending) {
         TRACE_EVENT0("cc", "CCFrameRateController::onTimerTickButMaxFramesPending");
         return;
     }
@@ -98,8 +114,7 @@ void CCFrameRateController::onTimerTick()
     if (m_client)
         m_client->vsyncTick();
 
-    if (!m_isTimeSourceThrottling
-        && (!m_maxFramesPending || m_numFramesPending < m_maxFramesPending))
+    if (m_swapBuffersCompleteSupported && !m_isTimeSourceThrottling && m_numFramesPending < m_maxFramesPending)
         postManualTick();
 }
 
@@ -116,11 +131,16 @@ void CCFrameRateController::onTimerFired()
 
 void CCFrameRateController::didBeginFrame()
 {
-    m_numFramesPending++;
+    if (m_swapBuffersCompleteSupported)
+        m_numFramesPending++;
+    else if (!m_isTimeSourceThrottling)
+        postManualTick();
 }
 
 void CCFrameRateController::didFinishFrame()
 {
+    ASSERT(m_swapBuffersCompleteSupported);
+
     m_numFramesPending--;
     if (!m_isTimeSourceThrottling)
         postManualTick();
diff --git a/cc/CCFrameRateController.h b/cc/CCFrameRateController.h
index 0aa3fdf..a609c38 100644
--- a/cc/CCFrameRateController.h
+++ b/cc/CCFrameRateController.h
@@ -50,6 +50,7 @@ public:
     double nextTickTimeIfActivated();
 
     void setTimebaseAndInterval(double timebase, double intervalSeconds);
+    void setSwapBuffersCompleteSupported(bool);
 
 protected:
     friend class CCFrameRateControllerTimeSourceAdapter;
@@ -66,6 +67,7 @@ protected:
     RefPtr<CCTimeSource> m_timeSource;
     OwnPtr<CCFrameRateControllerTimeSourceAdapter> m_timeSourceClientAdapter;
     bool m_active;
+    bool m_swapBuffersCompleteSupported;
 
     // Members for unthrottled frame-rate.
     bool m_isTimeSourceThrottling;
diff --git a/cc/CCLayerTreeHost.cpp b/cc/CCLayerTreeHost.cpp
index f236963..e126f15 100644
--- a/cc/CCLayerTreeHost.cpp
+++ b/cc/CCLayerTreeHost.cpp
@@ -638,7 +638,7 @@ void CCLayerTreeHost::applyScrollAndScale(const CCScrollAndScaleSet& info)
         if (layer == rootScrollLayer)
             rootScrollDelta += info.scrolls[i].scrollDelta;
         else
-            layer->scrollBy(info.scrolls[i].scrollDelta);
+            layer->setScrollPosition(layer->scrollPosition() + info.scrolls[i].scrollDelta);
     }
     if (!rootScrollDelta.isZero() || info.pageScaleDelta != 1)
         m_client->applyScrollAndScale(rootScrollDelta, info.pageScaleDelta);
diff --git a/cc/CCLayerTreeHostImpl.cpp b/cc/CCLayerTreeHostImpl.cpp
index a06bff9..9c78cff 100644
--- a/cc/CCLayerTreeHostImpl.cpp
+++ b/cc/CCLayerTreeHostImpl.cpp
@@ -148,6 +148,10 @@ void CCLayerTreeHostImpl::commitComplete()
 
 bool CCLayerTreeHostImpl::canDraw()
 {
+    // Note: If you are changing this function or any other function that might
+    // affect the result of canDraw, make sure to call m_client->onCanDrawStateChanged
+    // in the proper places and update the notifyIfCanDrawChanged test.
+
     if (!m_rootLayerImpl) {
         TRACE_EVENT_INSTANT0("cc", "CCLayerTreeHostImpl::canDraw no root layer");
         return false;
@@ -510,6 +514,7 @@ void CCLayerTreeHostImpl::releaseContentsTextures()
     m_resourceProvider->deleteOwnedResources(CCRenderer::ContentPool);
     m_contentsTexturesPurged = true;
     m_client->setNeedsCommitOnImplThread();
+    m_client->onCanDrawStateChanged(canDraw());
 }
 
 void CCLayerTreeHostImpl::setMemoryAllocationLimitBytes(size_t bytes)
@@ -649,6 +654,8 @@ void CCLayerTreeHostImpl::setRootLayer(PassOwnPtr<CCLayerImpl> layer)
         m_currentlyScrollingLayerImpl = CCLayerTreeHostCommon::findLayerInSubtree(m_rootLayerImpl.get(), m_scrollingLayerIdFromPreviousTree);
 
     m_scrollingLayerIdFromPreviousTree = -1;
+
+    m_client->onCanDrawStateChanged(canDraw());
 }
 
 PassOwnPtr<CCLayerImpl> CCLayerTreeHostImpl::detachLayerTree()
@@ -711,9 +718,17 @@ bool CCLayerTreeHostImpl::initializeRenderer(PassOwnPtr<CCGraphicsContext> conte
     if (!m_visible && m_renderer)
          m_renderer->setVisible(m_visible);
 
+    m_client->onCanDrawStateChanged(canDraw());
+
     return m_renderer;
 }
 
+void CCLayerTreeHostImpl::resetContentsTexturesPurged()
+{
+    m_contentsTexturesPurged = false;
+    m_client->onCanDrawStateChanged(canDraw());
+}
+
 void CCLayerTreeHostImpl::setViewportSize(const IntSize& layoutViewportSize, const IntSize& deviceViewportSize)
 {
     if (layoutViewportSize == m_layoutViewportSize && deviceViewportSize == m_deviceViewportSize)
@@ -726,6 +741,8 @@ void CCLayerTreeHostImpl::setViewportSize(const IntSize& layoutViewportSize, con
 
     if (m_renderer)
         m_renderer->viewportChanged();
+
+    m_client->onCanDrawStateChanged(canDraw());
 }
 
 static void adjustScrollsForPageScaleChange(CCLayerImpl* layerImpl, float pageScaleChange)
diff --git a/cc/CCLayerTreeHostImpl.h b/cc/CCLayerTreeHostImpl.h
index 44a3cae..4061d11 100644
--- a/cc/CCLayerTreeHostImpl.h
+++ b/cc/CCLayerTreeHostImpl.h
@@ -37,6 +37,7 @@ public:
     virtual void didLoseContextOnImplThread() = 0;
     virtual void onSwapBuffersCompleteOnImplThread() = 0;
     virtual void onVSyncParametersChanged(double monotonicTimebase, double intervalInSeconds) = 0;
+    virtual void onCanDrawStateChanged(bool canDraw) = 0;
     virtual void setNeedsRedrawOnImplThread() = 0;
     virtual void setNeedsCommitOnImplThread() = 0;
     virtual void postAnimationEventsToMainThreadOnImplThread(PassOwnPtr<CCAnimationEventsVector>, double wallClockTime) = 0;
@@ -140,7 +141,7 @@ public:
     void setSourceFrameNumber(int frameNumber) { m_sourceFrameNumber = frameNumber; }
 
     bool contentsTexturesPurged() const { return m_contentsTexturesPurged; }
-    void resetContentsTexturesPurged() { m_contentsTexturesPurged = false; }
+    void resetContentsTexturesPurged();
     size_t memoryAllocationLimitBytes() const { return m_memoryAllocationLimitBytes; }
 
     void setViewportSize(const IntSize& layoutViewportSize, const IntSize& deviceViewportSize);
diff --git a/cc/CCLayerTreeHostImplTest.cpp b/cc/CCLayerTreeHostImplTest.cpp
index f46cfda..8dc6752 100644
--- a/cc/CCLayerTreeHostImplTest.cpp
+++ b/cc/CCLayerTreeHostImplTest.cpp
@@ -50,7 +50,8 @@ namespace {
 class CCLayerTreeHostImplTest : public testing::Test, public CCLayerTreeHostImplClient {
 public:
     CCLayerTreeHostImplTest()
-        : m_didRequestCommit(false)
+        : m_onCanDrawStateChangedCalled(false)
+        , m_didRequestCommit(false)
         , m_didRequestRedraw(false)
     {
         CCLayerTreeSettings settings;
@@ -64,6 +65,7 @@ public:
     virtual void didLoseContextOnImplThread() OVERRIDE { }
     virtual void onSwapBuffersCompleteOnImplThread() OVERRIDE { }
     virtual void onVSyncParametersChanged(double, double) OVERRIDE { }
+    virtual void onCanDrawStateChanged(bool canDraw) OVERRIDE { m_onCanDrawStateChangedCalled = true; }
     virtual void setNeedsRedrawOnImplThread() OVERRIDE { m_didRequestRedraw = true; }
     virtual void setNeedsCommitOnImplThread() OVERRIDE { m_didRequestCommit = true; }
     virtual void postAnimationEventsToMainThreadOnImplThread(PassOwnPtr<CCAnimationEventsVector>, double wallClockTime) OVERRIDE { }
@@ -165,6 +167,7 @@ protected:
     DebugScopedSetMainThreadBlocked m_alwaysMainThreadBlocked;
 
     OwnPtr<CCLayerTreeHostImpl> m_hostImpl;
+    bool m_onCanDrawStateChangedCalled;
     bool m_didRequestCommit;
     bool m_didRequestRedraw;
     CCScopedSettings m_scopedSettings;
@@ -175,6 +178,53 @@ public:
     virtual bool makeContextCurrent() { return false; }
 };
 
+TEST_F(CCLayerTreeHostImplTest, notifyIfCanDrawChanged)
+{
+    // Note: It is not possible to disable the renderer once it has been set,
+    // so we do not need to test that disabling the renderer notifies us
+    // that canDraw changed.
+    EXPECT_FALSE(m_hostImpl->canDraw());
+    m_onCanDrawStateChangedCalled = false;
+
+    setupScrollAndContentsLayers(IntSize(100, 100));
+    EXPECT_TRUE(m_hostImpl->canDraw());
+    EXPECT_TRUE(m_onCanDrawStateChangedCalled);
+    m_onCanDrawStateChangedCalled = false;
+
+    // Toggle the root layer to make sure it toggles canDraw
+    m_hostImpl->setRootLayer(adoptPtr<CCLayerImpl>(0));
+    EXPECT_FALSE(m_hostImpl->canDraw());
+    EXPECT_TRUE(m_onCanDrawStateChangedCalled);
+    m_onCanDrawStateChangedCalled = false;
+
+    setupScrollAndContentsLayers(IntSize(100, 100));
+    EXPECT_TRUE(m_hostImpl->canDraw());
+    EXPECT_TRUE(m_onCanDrawStateChangedCalled);
+    m_onCanDrawStateChangedCalled = false;
+
+    // Toggle the device viewport size to make sure it toggles canDraw.
+    m_hostImpl->setViewportSize(IntSize(100, 100), IntSize(0, 0));
+    EXPECT_FALSE(m_hostImpl->canDraw());
+    EXPECT_TRUE(m_onCanDrawStateChangedCalled);
+    m_onCanDrawStateChangedCalled = false;
+
+    m_hostImpl->setViewportSize(IntSize(100, 100), IntSize(100, 100));
+    EXPECT_TRUE(m_hostImpl->canDraw());
+    EXPECT_TRUE(m_onCanDrawStateChangedCalled);
+    m_onCanDrawStateChangedCalled = false;
+
+    // Toggle contents textures purged to make sure it toggles canDraw
+    m_hostImpl->releaseContentsTextures();
+    EXPECT_FALSE(m_hostImpl->canDraw());
+    EXPECT_TRUE(m_onCanDrawStateChangedCalled);
+    m_onCanDrawStateChangedCalled = false;
+
+    m_hostImpl->resetContentsTexturesPurged();
+    EXPECT_TRUE(m_hostImpl->canDraw());
+    EXPECT_TRUE(m_onCanDrawStateChangedCalled);
+    m_onCanDrawStateChangedCalled = false;
+}
+
 TEST_F(CCLayerTreeHostImplTest, scrollDeltaNoLayers)
 {
     ASSERT_FALSE(m_hostImpl->rootLayer());
diff --git a/cc/CCLayerTreeHostTest.cpp b/cc/CCLayerTreeHostTest.cpp
index 4debcb1..489de86 100644
--- a/cc/CCLayerTreeHostTest.cpp
+++ b/cc/CCLayerTreeHostTest.cpp
@@ -21,6 +21,8 @@
 #include "FakeWebCompositorOutputSurface.h"
 #include <gmock/gmock.h>
 #include <public/Platform.h>
+#include <public/WebLayerScrollClient.h>
+#include <public/WebSize.h>
 #include <wtf/MainThread.h>
 #include <wtf/OwnArrayPtr.h>
 
@@ -2192,7 +2194,7 @@ private:
 
 SINGLE_AND_MULTI_THREAD_TEST_F(CCLayerTreeHostTestLayerAddedWithAnimation)
 
-class CCLayerTreeHostTestScrollChildLayer : public CCLayerTreeHostTest, public LayerChromiumScrollDelegate {
+class CCLayerTreeHostTestScrollChildLayer : public CCLayerTreeHostTest, public WebLayerScrollClient {
 public:
     CCLayerTreeHostTestScrollChildLayer()
         : m_scrollAmount(2, 1)
@@ -2215,7 +2217,7 @@ public:
         m_rootScrollLayer->setMaxScrollPosition(IntSize(100, 100));
         m_layerTreeHost->rootLayer()->addChild(m_rootScrollLayer);
         m_childLayer = ContentLayerChromium::create(&m_mockDelegate);
-        m_childLayer->setLayerScrollDelegate(this);
+        m_childLayer->setLayerScrollClient(this);
         m_childLayer->setBounds(IntSize(50, 50));
         m_childLayer->setIsDrawable(true);
         m_childLayer->setScrollable(true);
@@ -2228,9 +2230,9 @@ public:
         postSetNeedsCommitToMainThread();
     }
 
-    virtual void didScroll(const IntSize& scrollDelta) OVERRIDE
+    virtual void didScroll() OVERRIDE
     {
-        m_reportedScrollAmount = scrollDelta;
+        m_finalScrollPosition = m_childLayer->scrollPosition();
     }
 
     virtual void applyScrollAndScale(const IntSize& scrollDelta, float) OVERRIDE
@@ -2260,12 +2262,12 @@ public:
 
     virtual void afterTest() OVERRIDE
     {
-        EXPECT_EQ(m_scrollAmount, m_reportedScrollAmount);
+        EXPECT_EQ(IntPoint(m_scrollAmount), m_finalScrollPosition);
     }
 
 private:
     const IntSize m_scrollAmount;
-    IntSize m_reportedScrollAmount;
+    IntPoint m_finalScrollPosition;
     MockContentLayerChromiumClient m_mockDelegate;
     RefPtr<LayerChromium> m_childLayer;
     RefPtr<LayerChromium> m_rootScrollLayer;
diff --git a/cc/CCScheduler.cpp b/cc/CCScheduler.cpp
index 1840b4a..457cf05 100644
--- a/cc/CCScheduler.cpp
+++ b/cc/CCScheduler.cpp
@@ -37,6 +37,16 @@ void CCScheduler::setVisible(bool visible)
     processScheduledActions();
 }
 
+void CCScheduler::setCanDraw(bool canDraw)
+{
+    m_stateMachine.setCanDraw(canDraw);
+
+    // Defer processScheduleActions so we don't recurse and commit/draw
+    // multiple frames. We can call processScheduledActions directly
+    // once it is no longer re-entrant.
+    m_frameRateController->setActive(m_stateMachine.vsyncCallbackNeeded());
+}
+
 void CCScheduler::setNeedsCommit()
 {
     m_stateMachine.setNeedsCommit();
@@ -86,6 +96,11 @@ void CCScheduler::setMaxFramesPending(int maxFramesPending)
     m_frameRateController->setMaxFramesPending(maxFramesPending);
 }
 
+void CCScheduler::setSwapBuffersCompleteSupported(bool supported)
+{
+    m_frameRateController->setSwapBuffersCompleteSupported(supported);
+}
+
 void CCScheduler::didSwapBuffersComplete()
 {
     TRACE_EVENT0("cc", "CCScheduler::didSwapBuffersComplete");
@@ -125,16 +140,10 @@ void CCScheduler::vsyncTick()
     m_stateMachine.didLeaveVSync();
 }
 
-CCSchedulerStateMachine::Action CCScheduler::nextAction()
-{
-    m_stateMachine.setCanDraw(m_client->canDraw());
-    return m_stateMachine.nextAction();
-}
-
 void CCScheduler::processScheduledActions()
 {
     // Early out so we don't spam TRACE_EVENTS with useless processScheduledActions.
-    if (nextAction() == CCSchedulerStateMachine::ACTION_NONE) {
+    if (m_stateMachine.nextAction() == CCSchedulerStateMachine::ACTION_NONE) {
         m_frameRateController->setActive(m_stateMachine.vsyncCallbackNeeded());
         return;
     }
@@ -143,7 +152,7 @@ void CCScheduler::processScheduledActions()
     // setNeedsCommit. Proceeed with caution.
     CCSchedulerStateMachine::Action action;
     do {
-        action = nextAction();
+        action = m_stateMachine.nextAction();
         m_stateMachine.updateState(action);
         TRACE_EVENT1("cc", "CCScheduler::processScheduledActions()", "action", action);
 
diff --git a/cc/CCScheduler.h b/cc/CCScheduler.h
index 10fce73..fb043ac 100644
--- a/cc/CCScheduler.h
+++ b/cc/CCScheduler.h
@@ -32,7 +32,6 @@ struct CCScheduledActionDrawAndSwapResult {
 
 class CCSchedulerClient {
 public:
-    virtual bool canDraw() = 0;
     virtual bool hasMoreResourceUpdates() const = 0;
 
     virtual void scheduledActionBeginFrame() = 0;
@@ -60,6 +59,7 @@ public:
     void setCanBeginFrame(bool);
 
     void setVisible(bool);
+    void setCanDraw(bool);
 
     void setNeedsCommit();
 
@@ -77,6 +77,7 @@ public:
     void beginFrameAborted();
 
     void setMaxFramesPending(int);
+    void setSwapBuffersCompleteSupported(bool);
     void didSwapBuffersComplete();
 
     void didLoseContext();
@@ -93,7 +94,6 @@ public:
 private:
     CCScheduler(CCSchedulerClient*, PassOwnPtr<CCFrameRateController>);
 
-    CCSchedulerStateMachine::Action nextAction();
     void processScheduledActions();
 
     CCSchedulerClient* m_client;
diff --git a/cc/CCSchedulerStateMachine.cpp b/cc/CCSchedulerStateMachine.cpp
index 323a188..94f755c 100644
--- a/cc/CCSchedulerStateMachine.cpp
+++ b/cc/CCSchedulerStateMachine.cpp
@@ -5,6 +5,8 @@
 #include "config.h"
 
 #include "CCSchedulerStateMachine.h"
+#include "TextStream.h"
+
 
 namespace WebCore {
 
@@ -24,13 +26,38 @@ CCSchedulerStateMachine::CCSchedulerStateMachine()
     , m_insideVSync(false)
     , m_visible(false)
     , m_canBeginFrame(false)
-    , m_canDraw(true)
+    , m_canDraw(false)
     , m_drawIfPossibleFailed(false)
     , m_textureState(LAYER_TEXTURE_STATE_UNLOCKED)
     , m_contextState(CONTEXT_ACTIVE)
 {
 }
 
+String CCSchedulerStateMachine::toString()
+{
+    TextStream ts;
+    ts << "m_commitState = " << m_commitState << "; ";
+    ts << "m_currentFrameNumber = " << m_currentFrameNumber << "; ";
+    ts << "m_lastFrameNumberWhereDrawWasCalled = " << m_lastFrameNumberWhereDrawWasCalled << "; ";
+    ts << "m_consecutiveFailedDraws = " << m_consecutiveFailedDraws << "; ";
+    ts << "m_maximumNumberOfFailedDrawsBeforeDrawIsForced = " << m_maximumNumberOfFailedDrawsBeforeDrawIsForced << "; ";
+    ts << "m_needsRedraw = " << m_needsRedraw << "; ";
+    ts << "m_needsForcedRedraw = " << m_needsForcedRedraw << "; ";
+    ts << "m_needsForcedRedrawAfterNextCommit = " << m_needsForcedRedrawAfterNextCommit << "; ";
+    ts << "m_needsCommit = " << m_needsCommit << "; ";
+    ts << "m_needsForcedCommit = " << m_needsForcedCommit << "; ";
+    ts << "m_mainThreadNeedsLayerTextures = " << m_mainThreadNeedsLayerTextures << "; ";
+    ts << "m_updateMoreResourcesPending = " << m_updateMoreResourcesPending << "; ";
+    ts << "m_insideVSync = " << m_insideVSync << "; ";
+    ts << "m_visible = " << m_visible << "; ";
+    ts << "m_canBeginFrame = " << m_canBeginFrame << "; ";
+    ts << "m_canDraw = " << m_canDraw << "; ";
+    ts << "m_drawIfPossibleFailed = " << m_drawIfPossibleFailed << "; ";
+    ts << "m_textureState = " << m_textureState << "; ";
+    ts << "m_contextState = " << m_contextState << "; ";
+    return ts.release();
+}
+
 bool CCSchedulerStateMachine::hasDrawnThisFrame() const
 {
     return m_currentFrameNumber == m_lastFrameNumberWhereDrawWasCalled;
@@ -210,14 +237,18 @@ void CCSchedulerStateMachine::setMainThreadNeedsLayerTextures()
 
 bool CCSchedulerStateMachine::vsyncCallbackNeeded() const
 {
-    if (!m_visible || m_contextState != CONTEXT_ACTIVE) {
-        if (m_needsForcedRedraw || m_commitState == COMMIT_STATE_UPDATING_RESOURCES)
-            return true;
+    // To prevent live-lock, we must always tick when updating resources.
+    if (m_updateMoreResourcesPending || m_commitState == COMMIT_STATE_UPDATING_RESOURCES)
+        return true;
 
+    // If we can't draw, don't tick until we are notified that we can draw again.
+    if (!m_canDraw)
         return false;
-    }
 
-    return m_needsRedraw || m_needsForcedRedraw || m_commitState == COMMIT_STATE_UPDATING_RESOURCES;
+    if (m_needsForcedRedraw)
+        return true;
+
+    return m_needsRedraw && m_visible && m_contextState == CONTEXT_ACTIVE;
 }
 
 void CCSchedulerStateMachine::didEnterVSync()
diff --git a/cc/CCSchedulerStateMachine.h b/cc/CCSchedulerStateMachine.h
index 279b716..5cd46a7 100644
--- a/cc/CCSchedulerStateMachine.h
+++ b/cc/CCSchedulerStateMachine.h
@@ -6,6 +6,7 @@
 #define CCSchedulerStateMachine_h
 
 #include <wtf/Noncopyable.h>
+#include <wtf/text/WTFString.h>
 
 namespace WebCore {
 
@@ -128,6 +129,8 @@ public:
     // Exposed for testing purposes.
     void setMaximumNumberOfFailedDrawsBeforeDrawIsForced(int);
 
+    String toString();
+
 protected:
     bool shouldDrawForced() const;
     bool drawSuspendedUntilCommit() const;
diff --git a/cc/CCSchedulerStateMachineTest.cpp b/cc/CCSchedulerStateMachineTest.cpp
index cc2165a..1342b5b 100644
--- a/cc/CCSchedulerStateMachineTest.cpp
+++ b/cc/CCSchedulerStateMachineTest.cpp
@@ -116,6 +116,7 @@ TEST(CCSchedulerStateMachineTest, TestNextActionBeginsFrameIfNeeded)
 TEST(CCSchedulerStateMachineTest, TestSetForcedRedrawDoesNotSetsNormalRedraw)
 {
     CCSchedulerStateMachine state;
+    state.setCanDraw(true);
     state.setNeedsForcedRedraw();
     EXPECT_FALSE(state.redrawPending());
     EXPECT_TRUE(state.vsyncCallbackNeeded());
@@ -126,6 +127,7 @@ TEST(CCSchedulerStateMachineTest, TestFailedDrawSetsNeedsCommitAndDoesNotDrawAga
     CCSchedulerStateMachine state;
     state.setCanBeginFrame(true);
     state.setVisible(true);
+    state.setCanDraw(true);
     state.setNeedsRedraw();
     EXPECT_TRUE(state.redrawPending());
     EXPECT_TRUE(state.vsyncCallbackNeeded());
@@ -151,6 +153,7 @@ TEST(CCSchedulerStateMachineTest, TestSetNeedsRedrawDuringFailedDrawDoesNotRemov
     CCSchedulerStateMachine state;
     state.setCanBeginFrame(true);
     state.setVisible(true);
+    state.setCanDraw(true);
     state.setNeedsRedraw();
     EXPECT_TRUE(state.redrawPending());
     EXPECT_TRUE(state.vsyncCallbackNeeded());
@@ -179,6 +182,7 @@ TEST(CCSchedulerStateMachineTest, TestCommitAfterFailedDrawAllowsDrawInSameFrame
     CCSchedulerStateMachine state;
     state.setCanBeginFrame(true);
     state.setVisible(true);
+    state.setCanDraw(true);
 
     // Start a commit.
     state.setNeedsCommit();
@@ -219,6 +223,7 @@ TEST(CCSchedulerStateMachineTest, TestCommitAfterFailedAndSuccessfulDrawDoesNotA
     CCSchedulerStateMachine state;
     state.setCanBeginFrame(true);
     state.setVisible(true);
+    state.setCanDraw(true);
 
     // Start a commit.
     state.setNeedsCommit();
@@ -270,6 +275,7 @@ TEST(CCSchedulerStateMachineTest, TestFailedDrawsWillEventuallyForceADrawAfterTh
     CCSchedulerStateMachine state;
     state.setCanBeginFrame(true);
     state.setVisible(true);
+    state.setCanDraw(true);
     state.setMaximumNumberOfFailedDrawsBeforeDrawIsForced(1);
 
     // Start a commit.
@@ -312,6 +318,7 @@ TEST(CCSchedulerStateMachineTest, TestFailedDrawIsRetriedNextVSync)
     CCSchedulerStateMachine state;
     state.setCanBeginFrame(true);
     state.setVisible(true);
+    state.setCanDraw(true);
 
     // Start a draw.
     state.setNeedsRedraw();
@@ -341,6 +348,7 @@ TEST(CCSchedulerStateMachineTest, TestDoestDrawTwiceInSameFrame)
 {
     CCSchedulerStateMachine state;
     state.setVisible(true);
+    state.setCanDraw(true);
     state.setNeedsRedraw();
     EXPECT_TRUE(state.vsyncCallbackNeeded());
     state.didEnterVSync();
@@ -393,6 +401,7 @@ TEST(CCSchedulerStateMachineTest, TestNextActionDrawsOnVSync)
     for (size_t i = 0; i < numCommitStates; ++i) {
         for (unsigned j = 0; j < 2; ++j) {
             StateMachine state;
+            state.setCanDraw(true);
             state.setCommitState(allCommitStates[i]);
             bool forcedDraw = j;
             if (!forcedDraw) {
@@ -505,6 +514,28 @@ TEST(CCSchedulerStateMachineTest, TestCanRedrawWithWaitingForFirstDrawMakesProgr
     EXPECT_EQ(CCSchedulerStateMachine::ACTION_BEGIN_FRAME, state.nextAction());
 }
 
+TEST(CCSchedulerStateMachineTest, TestVsyncCallbackNeededOnCanDrawAndResourceUpdates)
+{
+    StateMachine state;
+    state.setCommitState(CCSchedulerStateMachine::COMMIT_STATE_WAITING_FOR_FIRST_DRAW);
+    state.setCanBeginFrame(true);
+    state.setNeedsCommit(true);
+    state.setNeedsRedraw(true);
+    state.setUpdateMoreResourcesPending(false);
+    state.setVisible(true);
+    state.setCanDraw(false);
+    EXPECT_FALSE(state.vsyncCallbackNeeded());
+
+    state.setUpdateMoreResourcesPending(true);
+    EXPECT_TRUE(state.vsyncCallbackNeeded());
+
+    state.setUpdateMoreResourcesPending(false);
+    EXPECT_FALSE(state.vsyncCallbackNeeded());
+
+    state.setCanDraw(true);
+    EXPECT_TRUE(state.vsyncCallbackNeeded());
+}
+
 TEST(CCSchedulerStateMachineTest, TestUpdates_NoRedraw_OneRoundOfUpdates)
 {
     StateMachine state;
@@ -512,6 +543,7 @@ TEST(CCSchedulerStateMachineTest, TestUpdates_NoRedraw_OneRoundOfUpdates)
     state.setNeedsRedraw(false);
     state.setUpdateMoreResourcesPending(false);
     state.setVisible(true);
+    state.setCanDraw(true);
 
     // Verify we begin update, both for vsync and not vsync.
     EXPECT_EQ(CCSchedulerStateMachine::ACTION_BEGIN_UPDATE_MORE_RESOURCES, state.nextAction());
@@ -540,6 +572,7 @@ TEST(CCSchedulerStateMachineTest, TestUpdates_NoRedraw_TwoRoundsOfUpdates)
     state.setNeedsRedraw(false);
     state.setUpdateMoreResourcesPending(false);
     state.setVisible(true);
+    state.setCanDraw(true);
 
     // Verify the update begins, both for vsync and not vsync.
     state.didEnterVSync();
@@ -579,6 +612,7 @@ TEST(CCSchedulerStateMachineTest, TestUpdates_NoRedraw_TwoRoundsOfUpdates)
 TEST(CCSchedulerStateMachineTest, TestVSyncNeededWhenUpdatesPendingButInvisible)
 {
     StateMachine state;
+    state.setCanDraw(true);
     state.setCommitState(CCSchedulerStateMachine::COMMIT_STATE_UPDATING_RESOURCES);
     state.setNeedsRedraw(false);
     state.setVisible(false);
@@ -596,6 +630,7 @@ TEST(CCSchedulerStateMachineTest, TestUpdates_WithRedraw_OneRoundOfUpdates)
     state.setNeedsRedraw(true);
     state.setUpdateMoreResourcesPending(false);
     state.setVisible(true);
+    state.setCanDraw(true);
     EXPECT_EQ(CCSchedulerStateMachine::ACTION_BEGIN_UPDATE_MORE_RESOURCES, state.nextAction());
 
     // Begin an update.
@@ -643,6 +678,7 @@ TEST(CCSchedulerStateMachineTest, TestSetNeedsCommitIsNotLost)
     state.setCanBeginFrame(true);
     state.setNeedsCommit(true);
     state.setVisible(true);
+    state.setCanDraw(true);
 
     // Begin the frame.
     EXPECT_EQ(CCSchedulerStateMachine::ACTION_BEGIN_FRAME, state.nextAction());
@@ -685,6 +721,7 @@ TEST(CCSchedulerStateMachineTest, TestFullCycle)
     StateMachine state;
     state.setCanBeginFrame(true);
     state.setVisible(true);
+    state.setCanDraw(true);
 
     // Start clean and set commit.
     state.setNeedsCommit(true);
@@ -733,6 +770,7 @@ TEST(CCSchedulerStateMachineTest, TestFullCycleWithCommitRequestInbetween)
     StateMachine state;
     state.setCanBeginFrame(true);
     state.setVisible(true);
+    state.setCanDraw(true);
 
     // Start clean and set commit.
     state.setNeedsCommit(true);
@@ -792,6 +830,7 @@ TEST(CCSchedulerStateMachineTest, TestGoesInvisibleBeforeBeginFrameCompletes)
     StateMachine state;
     state.setCanBeginFrame(true);
     state.setVisible(true);
+    state.setCanDraw(true);
 
     // Start clean and set commit.
     state.setNeedsCommit(true);
@@ -830,6 +869,7 @@ TEST(CCSchedulerStateMachineTest, TestContextLostWhenCompletelyIdle)
     StateMachine state;
     state.setCanBeginFrame(true);
     state.setVisible(true);
+    state.setCanDraw(true);
 
     state.didLoseContext();
 
@@ -852,6 +892,7 @@ TEST(CCSchedulerStateMachineTest, TestContextLostWhenIdleAndCommitRequestedWhile
     StateMachine state;
     state.setCanBeginFrame(true);
     state.setVisible(true);
+    state.setCanDraw(true);
 
     state.didLoseContext();
 
@@ -888,6 +929,7 @@ TEST(CCSchedulerStateMachineTest, TestContextLostWhileCommitInProgress)
     StateMachine state;
     state.setCanBeginFrame(true);
     state.setVisible(true);
+    state.setCanDraw(true);
 
     // Get a commit in flight.
     state.setNeedsCommit(true);
@@ -929,6 +971,7 @@ TEST(CCSchedulerStateMachineTest, TestContextLostWhileCommitInProgressAndAnother
     StateMachine state;
     state.setCanBeginFrame(true);
     state.setVisible(true);
+    state.setCanDraw(true);
 
     // Get a commit in flight.
     state.setNeedsCommit(true);
@@ -979,6 +1022,7 @@ TEST(CCSchedulerStateMachineTest, TestFinishAllRenderingWhileContextLost)
 {
     StateMachine state;
     state.setVisible(true);
+    state.setCanDraw(true);
 
     // Cause a lost context lost.
     state.didLoseContext();
@@ -1017,6 +1061,7 @@ TEST(CCSchedulerStateMachineTest, TestBeginFrameWhenCanBeginFrameFalseAndForceCo
 {
     StateMachine state;
     state.setVisible(true);
+    state.setCanDraw(true);
     state.setNeedsCommit(true);
     state.setNeedsForcedCommit(true);
     EXPECT_EQ(CCSchedulerStateMachine::ACTION_BEGIN_FRAME, state.nextAction());
@@ -1049,6 +1094,7 @@ TEST(CCSchedulerStateMachineTest, TestBeginFrameWhenContextLost)
     StateMachine state;
     state.setCanBeginFrame(true);
     state.setVisible(true);
+    state.setCanDraw(true);
     state.setNeedsCommit(true);
     state.setNeedsForcedCommit(true);
     state.didLoseContext();
diff --git a/cc/CCSchedulerTest.cpp b/cc/CCSchedulerTest.cpp
index ec68c71..ebd86dd 100644
--- a/cc/CCSchedulerTest.cpp
+++ b/cc/CCSchedulerTest.cpp
@@ -24,14 +24,12 @@ public:
     {
         m_actions.clear();
         m_hasMoreResourceUpdates = false;
-        m_canDraw = true;
         m_drawWillHappen = true;
         m_swapWillHappenIfDrawHappens = true;
         m_numDraws = 0;
     }
 
     void setHasMoreResourceUpdates(bool b) { m_hasMoreResourceUpdates = b; }
-    void setCanDraw(bool b) { m_canDraw = b; }
 
     int numDraws() const { return m_numDraws; }
     int numActions() const { return static_cast<int>(m_actions.size()); }
@@ -45,8 +43,8 @@ public:
         return false;
     }
 
-    virtual bool canDraw() OVERRIDE { return m_canDraw; }
     virtual bool hasMoreResourceUpdates() const OVERRIDE { return m_hasMoreResourceUpdates; }
+
     virtual void scheduledActionBeginFrame() OVERRIDE { m_actions.push_back("scheduledActionBeginFrame"); }
     virtual CCScheduledActionDrawAndSwapResult scheduledActionDrawAndSwapIfPossible() OVERRIDE
     {
@@ -71,7 +69,6 @@ public:
 
 protected:
     bool m_hasMoreResourceUpdates;
-    bool m_canDraw;
     bool m_drawWillHappen;
     bool m_swapWillHappenIfDrawHappens;
     int m_numDraws;
@@ -85,6 +82,7 @@ TEST(CCSchedulerTest, RequestCommit)
     OwnPtr<CCScheduler> scheduler = CCScheduler::create(&client, adoptPtr(new CCFrameRateController(timeSource)));
     scheduler->setCanBeginFrame(true);
     scheduler->setVisible(true);
+    scheduler->setCanDraw(true);
 
     // SetNeedsCommit should begin the frame.
     scheduler->setNeedsCommit();
@@ -119,6 +117,7 @@ TEST(CCSchedulerTest, RequestCommitAfterBeginFrame)
     OwnPtr<CCScheduler> scheduler = CCScheduler::create(&client, adoptPtr(new CCFrameRateController(timeSource)));
     scheduler->setCanBeginFrame(true);
     scheduler->setVisible(true);
+    scheduler->setCanDraw(true);
 
     // SetNedsCommit should begin the frame.
     scheduler->setNeedsCommit();
@@ -152,6 +151,7 @@ TEST(CCSchedulerTest, TextureAcquisitionCollision)
     OwnPtr<CCScheduler> scheduler = CCScheduler::create(&client, adoptPtr(new CCFrameRateController(timeSource)));
     scheduler->setCanBeginFrame(true);
     scheduler->setVisible(true);
+    scheduler->setCanDraw(true);
 
     scheduler->setNeedsCommit();
     scheduler->setMainThreadNeedsLayerTextures();
@@ -190,6 +190,7 @@ TEST(CCSchedulerTest, VisibilitySwitchWithTextureAcquisition)
     OwnPtr<CCScheduler> scheduler = CCScheduler::create(&client, adoptPtr(new CCFrameRateController(timeSource)));
     scheduler->setCanBeginFrame(true);
     scheduler->setVisible(true);
+    scheduler->setCanDraw(true);
 
     scheduler->setNeedsCommit();
     scheduler->beginFrameComplete();
@@ -253,6 +254,7 @@ TEST(CCSchedulerTest, RequestRedrawInsideDraw)
     client.setScheduler(scheduler.get());
     scheduler->setCanBeginFrame(true);
     scheduler->setVisible(true);
+    scheduler->setCanDraw(true);
 
     scheduler->setNeedsRedraw();
     EXPECT_TRUE(scheduler->redrawPending());
@@ -279,6 +281,7 @@ TEST(CCSchedulerTest, RequestRedrawInsideFailedDraw)
     client.setScheduler(scheduler.get());
     scheduler->setCanBeginFrame(true);
     scheduler->setVisible(true);
+    scheduler->setCanDraw(true);
     client.setDrawWillHappen(false);
 
     scheduler->setNeedsRedraw();
@@ -351,6 +354,7 @@ TEST(CCSchedulerTest, RequestCommitInsideDraw)
     client.setScheduler(scheduler.get());
     scheduler->setCanBeginFrame(true);
     scheduler->setVisible(true);
+    scheduler->setCanDraw(true);
 
     scheduler->setNeedsRedraw();
     EXPECT_TRUE(scheduler->redrawPending());
@@ -378,6 +382,7 @@ TEST(CCSchedulerTest, RequestCommitInsideFailedDraw)
     client.setScheduler(scheduler.get());
     scheduler->setCanBeginFrame(true);
     scheduler->setVisible(true);
+    scheduler->setCanDraw(true);
     client.setDrawWillHappen(false);
 
     scheduler->setNeedsRedraw();
@@ -420,6 +425,7 @@ TEST(CCSchedulerTest, NoBeginFrameWhenDrawFails)
     client.setScheduler(scheduler.get());
     scheduler->setCanBeginFrame(true);
     scheduler->setVisible(true);
+    scheduler->setCanDraw(true);
 
     EXPECT_EQ(0, controllerPtr->numFramesPending());
 
diff --git a/cc/CCSingleThreadProxy.h b/cc/CCSingleThreadProxy.h
index 02981d1..95f8743 100644
--- a/cc/CCSingleThreadProxy.h
+++ b/cc/CCSingleThreadProxy.h
@@ -49,6 +49,7 @@ public:
     virtual void didLoseContextOnImplThread() OVERRIDE { }
     virtual void onSwapBuffersCompleteOnImplThread() OVERRIDE { ASSERT_NOT_REACHED(); }
     virtual void onVSyncParametersChanged(double monotonicTimebase, double intervalInSeconds) OVERRIDE { }
+    virtual void onCanDrawStateChanged(bool canDraw) OVERRIDE { }
     virtual void setNeedsRedrawOnImplThread() OVERRIDE { m_layerTreeHost->scheduleComposite(); }
     virtual void setNeedsCommitOnImplThread() OVERRIDE { m_layerTreeHost->scheduleComposite(); }
     virtual void postAnimationEventsToMainThreadOnImplThread(PassOwnPtr<CCAnimationEventsVector>, double wallClockTime) OVERRIDE;
diff --git a/cc/CCThreadProxy.cpp b/cc/CCThreadProxy.cpp
index 9255010..184ec51 100644
--- a/cc/CCThreadProxy.cpp
+++ b/cc/CCThreadProxy.cpp
@@ -332,6 +332,13 @@ void CCThreadProxy::onVSyncParametersChanged(double monotonicTimebase, double in
     m_schedulerOnImplThread->setTimebaseAndInterval(monotonicTimebase, intervalInSeconds);
 }
 
+void CCThreadProxy::onCanDrawStateChanged(bool canDraw)
+{
+    ASSERT(isImplThread());
+    TRACE_EVENT1("cc", "CCThreadProxy::onCanDrawStateChanged", "canDraw", canDraw);
+    m_schedulerOnImplThread->setCanDraw(canDraw);
+}
+
 void CCThreadProxy::setNeedsCommitOnImplThread()
 {
     ASSERT(isImplThread());
@@ -522,8 +529,10 @@ void CCThreadProxy::beginFrame()
     m_commitRequestSentToImplThread = false;
     m_forcedCommitRequested = false;
 
-    if (!m_layerTreeHost->initializeRendererIfNeeded())
+    if (!m_layerTreeHost->initializeRendererIfNeeded()) {
+        TRACE_EVENT0("cc", "EarlyOut_InitializeFailed");
         return;
+    }
 
     if (request->contentsTexturesWereDeleted)
         m_layerTreeHost->evictAllContentTextures();
@@ -573,6 +582,7 @@ void CCThreadProxy::beginFrameCompleteOnImplThread(CCCompletionEvent* completion
     ASSERT(m_schedulerOnImplThread->commitPending());
 
     if (!m_layerTreeHostImpl) {
+        TRACE_EVENT0("cc", "EarlyOut_NoLayerTree");
         completion->signal();
         return;
     }
@@ -610,14 +620,6 @@ bool CCThreadProxy::hasMoreResourceUpdates() const
     return m_currentTextureUpdateControllerOnImplThread->hasMoreUpdates();
 }
 
-bool CCThreadProxy::canDraw()
-{
-    ASSERT(isImplThread());
-    if (!m_layerTreeHostImpl)
-        return false;
-    return m_layerTreeHostImpl->canDraw();
-}
-
 void CCThreadProxy::scheduledActionUpdateMoreResources(double monotonicTimeLimit)
 {
     TRACE_EVENT0("cc", "CCThreadProxy::scheduledActionUpdateMoreResources");
@@ -868,8 +870,8 @@ void CCThreadProxy::initializeRendererOnImplThread(CCCompletionEvent* completion
     *initializeSucceeded = m_layerTreeHostImpl->initializeRenderer(m_contextBeforeInitializationOnImplThread.release(), textureUploader);
     if (*initializeSucceeded) {
         *capabilities = m_layerTreeHostImpl->rendererCapabilities();
-        if (capabilities->usingSwapCompleteCallback)
-            m_schedulerOnImplThread->setMaxFramesPending(2);
+        m_schedulerOnImplThread->setSwapBuffersCompleteSupported(
+                capabilities->usingSwapCompleteCallback);
     }
 
     completion->signal();
diff --git a/cc/CCThreadProxy.h b/cc/CCThreadProxy.h
index c488dcb..bf9c378 100644
--- a/cc/CCThreadProxy.h
+++ b/cc/CCThreadProxy.h
@@ -58,13 +58,14 @@ public:
     virtual void didLoseContextOnImplThread() OVERRIDE;
     virtual void onSwapBuffersCompleteOnImplThread() OVERRIDE;
     virtual void onVSyncParametersChanged(double monotonicTimebase, double intervalInSeconds) OVERRIDE;
+    virtual void onCanDrawStateChanged(bool canDraw) OVERRIDE;
     virtual void setNeedsRedrawOnImplThread() OVERRIDE;
     virtual void setNeedsCommitOnImplThread() OVERRIDE;
     virtual void postAnimationEventsToMainThreadOnImplThread(PassOwnPtr<CCAnimationEventsVector>, double wallClockTime) OVERRIDE;
 
     // CCSchedulerClient implementation
-    virtual bool canDraw() OVERRIDE;
     virtual bool hasMoreResourceUpdates() const OVERRIDE;
+
     virtual void scheduledActionBeginFrame() OVERRIDE;
     virtual CCScheduledActionDrawAndSwapResult scheduledActionDrawAndSwapIfPossible() OVERRIDE;
     virtual CCScheduledActionDrawAndSwapResult scheduledActionDrawAndSwapForced() OVERRIDE;
diff --git a/cc/LayerChromium.cpp b/cc/LayerChromium.cpp
index 8dc15ad..da4b002 100644
--- a/cc/LayerChromium.cpp
+++ b/cc/LayerChromium.cpp
@@ -16,6 +16,8 @@
 #include "TextStream.h"
 
 #include <public/WebAnimationDelegate.h>
+#include <public/WebLayerScrollClient.h>
+#include <public/WebSize.h>
 
 using namespace std;
 using WebKit::WebTransformationMatrix;
@@ -65,7 +67,7 @@ LayerChromium::LayerChromium()
     , m_screenSpaceTransformIsAnimating(false)
     , m_contentsScale(1.0)
     , m_layerAnimationDelegate(0)
-    , m_layerScrollDelegate(0)
+    , m_layerScrollClient(0)
 {
     if (m_layerId < 0) {
         s_nextLayerId = 1;
@@ -369,6 +371,8 @@ void LayerChromium::setScrollPosition(const IntPoint& scrollPosition)
     if (m_scrollPosition == scrollPosition)
         return;
     m_scrollPosition = scrollPosition;
+    if (m_layerScrollClient)
+        m_layerScrollClient->didScroll();
     setNeedsCommit();
 }
 
@@ -413,13 +417,6 @@ void LayerChromium::setNonFastScrollableRegion(const Region& region)
     setNeedsCommit();
 }
 
-void LayerChromium::scrollBy(const IntSize& scrollDelta)
-{
-    setScrollPosition(scrollPosition() + scrollDelta);
-    if (m_layerScrollDelegate)
-        m_layerScrollDelegate->didScroll(scrollDelta);
-}
-
 void LayerChromium::setDrawCheckerboardForMissingTiles(bool checkerboard)
 {
     if (m_drawCheckerboardForMissingTiles == checkerboard)
diff --git a/cc/LayerChromium.h b/cc/LayerChromium.h
index 273bf8e..aad1fe2 100644
--- a/cc/LayerChromium.h
+++ b/cc/LayerChromium.h
@@ -28,6 +28,7 @@
 
 namespace WebKit {
 class WebAnimationDelegate;
+class WebLayerScrollClient;
 }
 
 namespace WebCore {
@@ -42,15 +43,6 @@ class ScrollbarLayerChromium;
 struct CCAnimationEvent;
 struct CCRenderingStats;
 
-// Delegate for handling scroll input for a LayerChromium.
-class LayerChromiumScrollDelegate {
-public:
-    virtual void didScroll(const IntSize&) = 0;
-
-protected:
-    virtual ~LayerChromiumScrollDelegate() { }
-};
-
 // Base class for composited layers. Special layer types are derived from
 // this class.
 class LayerChromium : public RefCounted<LayerChromium>, public CCLayerAnimationControllerClient {
@@ -149,8 +141,7 @@ public:
     const Region& nonFastScrollableRegion() { return m_nonFastScrollableRegion; }
     void setNonFastScrollableRegion(const Region&);
     void setNonFastScrollableRegionChanged() { m_nonFastScrollableRegionChanged = true; }
-    void setLayerScrollDelegate(LayerChromiumScrollDelegate* layerScrollDelegate) { m_layerScrollDelegate = layerScrollDelegate; }
-    void scrollBy(const IntSize&);
+    void setLayerScrollClient(WebKit::WebLayerScrollClient* layerScrollClient) { m_layerScrollClient = layerScrollClient; }
 
     void setDrawCheckerboardForMissingTiles(bool);
     bool drawCheckerboardForMissingTiles() const { return m_drawCheckerboardForMissingTiles; }
@@ -370,7 +361,7 @@ private:
     float m_contentsScale;
 
     WebKit::WebAnimationDelegate* m_layerAnimationDelegate;
-    LayerChromiumScrollDelegate* m_layerScrollDelegate;
+    WebKit::WebLayerScrollClient* m_layerScrollClient;
 };
 
 void sortLayers(Vector<RefPtr<LayerChromium> >::iterator, Vector<RefPtr<LayerChromium> >::iterator, void*);