Communicate MT changes to impl-only scroll offset animations

third_party/WebKit/Source/platform/animation/CompositorAnimationTimeline.cpp

Index: third_party/WebKit/Source/platform/animation/CompositorAnimationTimeline.cpp
diff --git a/third_party/WebKit/Source/platform/animation/CompositorAnimationTimeline.cpp b/third_party/WebKit/Source/platform/animation/CompositorAnimationTimeline.cpp
index 4b2199c36ac216551d86ecfae72c4559a58016de..4e39e6e98827eb8e1bdd311c72b6cefa5a4f36f3 100644
--- a/third_party/WebKit/Source/platform/animation/CompositorAnimationTimeline.cpp
+++ b/third_party/WebKit/Source/platform/animation/CompositorAnimationTimeline.cpp
@@ -6,13 +6,15 @@
 
 #include "cc/animation/animation_host.h"
 #include "cc/animation/animation_id_provider.h"
+#include "platform/animation/CompositorAnimationHost.h"
 #include "platform/animation/CompositorAnimationPlayer.h"
 #include "platform/animation/CompositorAnimationPlayerClient.h"
 
 namespace blink {
 
 CompositorAnimationTimeline::CompositorAnimationTimeline()
-    : m_animationTimeline(cc::AnimationTimeline::Create(cc::AnimationIdProvider::NextTimelineId()))
+    : m_compositorAnimationHost(nullptr)
+    , m_animationTimeline(cc::AnimationTimeline::Create(cc::AnimationIdProvider::NextTimelineId()))
 {
 }
 
@@ -29,6 +31,19 @@ cc::AnimationTimeline* CompositorAnimationTimeline::animationTimeline() const
     return m_animationTimeline.get();
 }
 
+CompositorAnimationHost* CompositorAnimationTimeline::compositorAnimationHost()
+{
+    if (!m_animationTimeline->animation_host())
+        return nullptr;
+
+    if (m_compositorAnimationHost && m_animationTimeline->animation_host() == m_compositorAnimationHost->animationHost())
+        return m_compositorAnimationHost.get();
+
+    m_compositorAnimationHost = base::WrapUnique(
+        new CompositorAnimationHost(m_animationTimeline->animation_host()));
+    return m_compositorAnimationHost.get();
+}
+
 void CompositorAnimationTimeline::playerAttached(const blink::CompositorAnimationPlayerClient& client)
 {
     if (client.compositorPlayer())