Scrollbar fade animation broken on Android regression resolved.

cc/trees/layer_tree_host_impl.h

Index: cc/trees/layer_tree_host_impl.h
diff --git a/cc/trees/layer_tree_host_impl.h b/cc/trees/layer_tree_host_impl.h
index 6d97f27511c28112ed55508cc8e9e0b4ccf27f20..8517101ce3ab477f75ab246af5880000944760e1 100644
--- a/cc/trees/layer_tree_host_impl.h
+++ b/cc/trees/layer_tree_host_impl.h
@@ -131,6 +131,38 @@ class LayerTreeHostImplClient {
   virtual ~LayerTreeHostImplClient() {}
 };
 
+// Used to cache scroll related variables that get reset while clearing
+// the currently scrolling layer. Cached values are restored in case of a
+// scrollBegin in inertial phase (fling) to latch the fling to its
+// corresponding scroll event.

[tdresser, 2016/10/26 15:38:18]

It doesn't latch the fling to the scroll event, it latches the fling to the
previously scrolling layer.

[sahel, 2016/10/26 18:47:45]

Done.

+class ScrollStateForFling {
+ public:
+  ScrollStateForFling() {
+    ScrollStateForFling(Layer::INVALID_ID, false, false, gfx::Vector2dF());
+  }
+  ScrollStateForFling(int scrolling_layer_id,
+                      bool did_lock_scrolling_layer,
+                      bool scroll_affects_scroll_handler,
+                      gfx::Vector2dF accumulated_root_overscroll)
+      : scrolling_layer_id_(scrolling_layer_id),
+        did_lock_scrolling_layer_(did_lock_scrolling_layer),
+        scroll_affects_scroll_handler_(scroll_affects_scroll_handler),
+        accumulated_root_overscroll_(accumulated_root_overscroll) {}
+
+  int scrollingLayerId() { return scrolling_layer_id_; }

[bokan, 2016/10/26 14:17:43]

nit: these methods should all be of the style scrolling_layer_id()

[sahel, 2016/10/26 18:47:45]

Done.

+  bool didLockScrollingLayer() { return did_lock_scrolling_layer_; }
+  bool scrollAffectsScrollHandler() { return scroll_affects_scroll_handler_; }
+  gfx::Vector2dF accumulatedRootOverscroll() {
+    return accumulated_root_overscroll_;
+  }
+
+ private:
+  int scrolling_layer_id_;
+  bool did_lock_scrolling_layer_;
+  bool scroll_affects_scroll_handler_;
+  gfx::Vector2dF accumulated_root_overscroll_;
+};
+
 // LayerTreeHostImpl owns the LayerImpl trees as well as associated rendering
 // state.
 class CC_EXPORT LayerTreeHostImpl
@@ -701,6 +733,13 @@ class CC_EXPORT LayerTreeHostImpl
   void SetCompositorContextVisibility(bool is_visible);
   void SetWorkerContextVisibility(bool is_visible);
 
+  // Cache & restore variables that get reset in ClearCurrentlyScrollingLayer.
+  // This is used to restore the variables' values in a scrollBegin event
+  // that is in inertial phase (a fling) to latch the event to its
+  // corresponding scroller.
+  void CacheScrollStateForFling();
+  LayerImpl* RestoreScrollStateForFling();
+
   using UIResourceMap = std::unordered_map<UIResourceId, UIResourceData>;
   UIResourceMap ui_resource_map_;
 
@@ -841,6 +880,8 @@ class CC_EXPORT LayerTreeHostImpl
   std::unique_ptr<PendingTreeDurationHistogramTimer>
       pending_tree_duration_timer_;
 
+  ScrollStateForFling cached_scroll_state_for_fling_;
+
   DISALLOW_COPY_AND_ASSIGN(LayerTreeHostImpl);
 };