Scrollbar fade animation broken on Android regression resolved.

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index 5b90fd12c5a679f7c2823aa1327898fe84ed435e..a17755bb29fa53ef2b4df84b18d0e6590a8d464f 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -240,7 +240,11 @@ LayerTreeHostImpl::LayerTreeHostImpl(
       requires_high_res_to_draw_(false),
       is_likely_to_require_a_draw_(false),
       has_valid_compositor_frame_sink_(false),
-      mutator_(nullptr) {
+      mutator_(nullptr),
+      cached_scroll_state_for_fling_(Layer::INVALID_ID,
+                                     did_lock_scrolling_layer_,
+                                     scroll_affects_scroll_handler_,
+                                     accumulated_root_overscroll_) {
   DCHECK(animation_host_);
   animation_host_->SetMutatorHostClient(this);
 
@@ -2642,49 +2646,55 @@ InputHandler::ScrollStatus LayerTreeHostImpl::ScrollBegin(
   scroll_status.main_thread_scrolling_reasons =
       MainThreadScrollingReason::kNotScrollingOnMain;
   TRACE_EVENT0("cc", "LayerTreeHostImpl::ScrollBegin");
-
+  LayerImpl* scrolling_layer_impl = nullptr;
   // On Mac a scroll begin with |inertial_phase| = true happens to handle a
-  // fling.
-  if (scroll_state->is_in_inertial_phase())
-    return FlingScrollBegin();
+  // fling. Also, touchpad fling starts are handled by calling ScrollBegin
+  // instead of FlingScrollBegin.
+  if (scroll_state->is_in_inertial_phase()) {
+    RestoreScrollStateForFling();
+    scrolling_layer_impl = active_tree_->CurrentlyScrollingLayer();
+  }
 
-  ClearCurrentlyScrollingLayer();
+  if (!scrolling_layer_impl) {
+    ClearCurrentlyScrollingLayer();
 
-  gfx::Point viewport_point(scroll_state->position_x(),
-                            scroll_state->position_y());
+    gfx::Point viewport_point(scroll_state->position_x(),
+                              scroll_state->position_y());
 
-  gfx::PointF device_viewport_point = gfx::ScalePoint(
-      gfx::PointF(viewport_point), active_tree_->device_scale_factor());
-  LayerImpl* layer_impl =
-      active_tree_->FindLayerThatIsHitByPoint(device_viewport_point);
-
-  if (layer_impl) {
-    LayerImpl* scroll_layer_impl =
-        active_tree_->FindFirstScrollingLayerOrScrollbarLayerThatIsHitByPoint(
-            device_viewport_point);
-    if (scroll_layer_impl &&
-        !HasScrollAncestor(layer_impl, scroll_layer_impl)) {
-      scroll_status.thread = SCROLL_UNKNOWN;
-      scroll_status.main_thread_scrolling_reasons =
-          MainThreadScrollingReason::kFailedHitTest;
-      return scroll_status;
+    gfx::PointF device_viewport_point = gfx::ScalePoint(
+        gfx::PointF(viewport_point), active_tree_->device_scale_factor());
+    LayerImpl* layer_impl =
+        active_tree_->FindLayerThatIsHitByPoint(device_viewport_point);
+
+    if (layer_impl) {
+      LayerImpl* scroll_layer_impl =
+          active_tree_->FindFirstScrollingLayerOrScrollbarLayerThatIsHitByPoint(
+              device_viewport_point);
+      if (scroll_layer_impl &&
+          !HasScrollAncestor(layer_impl, scroll_layer_impl)) {
+        scroll_status.thread = SCROLL_UNKNOWN;
+        scroll_status.main_thread_scrolling_reasons =
+            MainThreadScrollingReason::kFailedHitTest;
+        return scroll_status;
+      }
     }
-  }
 
-  bool scroll_on_main_thread = false;
-  LayerImpl* scrolling_layer_impl = FindScrollLayerForDeviceViewportPoint(
-      device_viewport_point, type, layer_impl, &scroll_on_main_thread,
-      &scroll_status.main_thread_scrolling_reasons);
+    bool scroll_on_main_thread = false;
+    scrolling_layer_impl = FindScrollLayerForDeviceViewportPoint(
+        device_viewport_point, type, layer_impl, &scroll_on_main_thread,
+        &scroll_status.main_thread_scrolling_reasons);
 
-  if (scrolling_layer_impl)
-    scroll_affects_scroll_handler_ =
-        scrolling_layer_impl->layer_tree_impl()->have_scroll_event_handlers();
+    if (scrolling_layer_impl) {
+      scroll_affects_scroll_handler_ =
+          scrolling_layer_impl->layer_tree_impl()->have_scroll_event_handlers();
+    }
 
-  if (scroll_on_main_thread) {
-    RecordCompositorSlowScrollMetric(type, MAIN_THREAD);
+    if (scroll_on_main_thread) {
+      RecordCompositorSlowScrollMetric(type, MAIN_THREAD);
 
-    scroll_status.thread = SCROLL_ON_MAIN_THREAD;
-    return scroll_status;
+      scroll_status.thread = SCROLL_ON_MAIN_THREAD;
+      return scroll_status;
+    }
   }
 
   return ScrollBeginImpl(scroll_state, scrolling_layer_impl, type);
@@ -2724,11 +2734,7 @@ InputHandler::ScrollStatus LayerTreeHostImpl::ScrollAnimatedBegin(
     ScrollStateData scroll_state_end_data;
     scroll_state_end_data.is_ending = true;
     ScrollState scroll_state_end(scroll_state_end_data);
-    // TODO(Sahel): Once the touchpad scroll latching for Non-mac devices is
-    // implemented, the current scrolling layer should not get cleared after
-    // each animation (crbug.com/526463).
     ScrollEnd(&scroll_state_end);
-    ClearCurrentlyScrollingLayer();
   }
   return scroll_status;
 }
@@ -2852,11 +2858,7 @@ InputHandler::ScrollStatus LayerTreeHostImpl::ScrollAnimated(
     }
   }
   scroll_state.set_is_ending(true);
-  // TODO(Sahel): Once the touchpad scroll latching for Non-mac devices is
-  // implemented, the current scrolling layer should not get cleared after
-  // each animation (crbug.com/526463).
   ScrollEnd(&scroll_state);
-  ClearCurrentlyScrollingLayer();
 
   return scroll_status;
 }
@@ -3164,6 +3166,11 @@ void LayerTreeHostImpl::SetSynchronousInputHandlerRootScrollOffset(
 }
 
 void LayerTreeHostImpl::ClearCurrentlyScrollingLayer() {
+  // Cached scrolling variables state is restored in a ScrollBegin with
+  // inertial phase (fling) to latch it to its corresponding scroll. When
+  // reseting a variable here, update ScrollStateForFling class as well
+  // to maintain the proper caching.
+  CacheScrollStateForFling();
   active_tree_->ClearCurrentlyScrollingLayer();
   did_lock_scrolling_layer_ = false;
   scroll_affects_scroll_handler_ = false;
@@ -3177,11 +3184,7 @@ void LayerTreeHostImpl::ScrollEnd(ScrollState* scroll_state) {
   DistributeScrollDelta(scroll_state);
   top_controls_manager_->ScrollEnd();
 
-  if (scroll_state->is_in_inertial_phase()) {
-    // Only clear the currently scrolling layer if we know the scroll is done.
-    // A non-inertial scroll end could be followed by an inertial scroll.
-    ClearCurrentlyScrollingLayer();
-  }
+  ClearCurrentlyScrollingLayer();
 }
 
 InputHandler::ScrollStatus LayerTreeHostImpl::FlingScrollBegin() {
@@ -4018,11 +4021,7 @@ void LayerTreeHostImpl::ScrollOffsetAnimationFinished() {
   // TODO(majidvp): We should pass in the original starting scroll position here
   ScrollStateData scroll_state_data;
   ScrollState scroll_state(scroll_state_data);
-  // TODO(Sahel): Once the touchpad scroll latching for Non-mac devices is
-  // implemented, the current scrolling layer should not get cleared after
-  // each animation (crbug.com/526463).
   ScrollEnd(&scroll_state);
-  ClearCurrentlyScrollingLayer();
 }
 
 gfx::ScrollOffset LayerTreeHostImpl::GetScrollOffsetForAnimation(
@@ -4090,4 +4089,23 @@ void LayerTreeHostImpl::SetWorkerContextVisibility(bool is_visible) {
   }
 }
 
+void LayerTreeHostImpl::CacheScrollStateForFling() {
+  int scrolling_layer_id = active_tree_->CurrentlyScrollingLayer()
+                               ? active_tree_->CurrentlyScrollingLayer()->id()
+                               : Layer::INVALID_ID;
+  cached_scroll_state_for_fling_ = ScrollStateForFling(
+      scrolling_layer_id, did_lock_scrolling_layer_,
+      scroll_affects_scroll_handler_, accumulated_root_overscroll_);
+}
+void LayerTreeHostImpl::RestoreScrollStateForFling() {
+  active_tree_->SetCurrentlyScrollingLayer(active_tree_->LayerById(
+      cached_scroll_state_for_fling_.scrolling_layer_id()));
+  did_lock_scrolling_layer_ =
+      cached_scroll_state_for_fling_.did_lock_scrolling_layer();
+  scroll_affects_scroll_handler_ =
+      cached_scroll_state_for_fling_.scroll_affects_scroll_handler();
+  accumulated_root_overscroll_ =
+      cached_scroll_state_for_fling_.accumulated_root_overscroll();
+}
+
 }  // namespace cc