Update from https://crrev.com/318214

cc/input/top_controls_manager.cc

Index: cc/input/top_controls_manager.cc
diff --git a/cc/input/top_controls_manager.cc b/cc/input/top_controls_manager.cc
index 615afb07056800b92d55ad38807fec7ce2212c65..7362805de99acba4c5caa3145f9f268df1778336 100644
--- a/cc/input/top_controls_manager.cc
+++ b/cc/input/top_controls_manager.cc
@@ -39,8 +39,8 @@ TopControlsManager::TopControlsManager(TopControlsManagerClient* client,
     : client_(client),
       animation_direction_(NO_ANIMATION),
       permitted_state_(BOTH),
-      current_scroll_delta_(0.f),
-      controls_scroll_begin_offset_(0.f),
+      accumulated_scroll_delta_(0.f),
+      baseline_content_offset_(0.f),
       top_controls_show_threshold_(top_controls_hide_threshold),
       top_controls_hide_threshold_(top_controls_show_threshold),
       pinch_gesture_active_(false) {
@@ -96,8 +96,7 @@ void TopControlsManager::UpdateTopControlsState(TopControlsState constraints,
 void TopControlsManager::ScrollBegin() {
   DCHECK(!pinch_gesture_active_);
   ResetAnimations();
-  current_scroll_delta_ = 0.f;
-  controls_scroll_begin_offset_ = ContentTopOffset();
+  ResetBaseline();
 }
 
 gfx::Vector2dF TopControlsManager::ScrollBy(
@@ -110,19 +109,17 @@ gfx::Vector2dF TopControlsManager::ScrollBy(
   else if (permitted_state_ == HIDDEN && pending_delta.y() < 0)
     return pending_delta;
 
-  current_scroll_delta_ += pending_delta.y();
+  accumulated_scroll_delta_ += pending_delta.y();
 
   float old_offset = ContentTopOffset();
   client_->SetCurrentTopControlsShownRatio(
-      (controls_scroll_begin_offset_ - current_scroll_delta_) /
+      (baseline_content_offset_ - accumulated_scroll_delta_) /
       TopControlsHeight());
 
   // If the controls are fully visible, treat the current position as the
   // new baseline even if the gesture didn't end.
-  if (TopControlsShownRatio() == 1.f) {
-    current_scroll_delta_ = 0.f;
-    controls_scroll_begin_offset_ = ContentTopOffset();
-  }
+  if (TopControlsShownRatio() == 1.f)
+    ResetBaseline();
 
   ResetAnimations();
 
@@ -149,6 +146,10 @@ void TopControlsManager::PinchEnd() {
   ScrollBegin();
 }
 
+void TopControlsManager::MainThreadHasStoppedFlinging() {
+  StartAnimationIfNecessary();
+}
+
 gfx::Vector2dF TopControlsManager::Animate(base::TimeTicks monotonic_time) {
   if (!top_controls_animation_ || !client_->HaveRootScrollLayer())
     return gfx::Vector2dF();
@@ -206,8 +207,8 @@ void TopControlsManager::StartAnimationIfNecessary() {
     // If we could be either showing or hiding, we determine which one to
     // do based on whether or not the total scroll delta was moving up or
     // down.
-    SetupAnimation(current_scroll_delta_ <= 0.f ? SHOWING_CONTROLS
-                                                : HIDING_CONTROLS);
+    SetupAnimation(accumulated_scroll_delta_ <= 0.f ? SHOWING_CONTROLS
+                                                    : HIDING_CONTROLS);
   }
 }
 
@@ -225,4 +226,9 @@ bool TopControlsManager::IsAnimationCompleteAtTime(base::TimeTicks time) {
   return false;
 }
 
+void TopControlsManager::ResetBaseline() {
+  accumulated_scroll_delta_ = 0.f;
+  baseline_content_offset_ = ContentTopOffset();
+}
+
 }  // namespace cc