CL for src perf tryjob to run smoothness.scrolling_tough_ad_cases benchmark on android-nexus5X plat…

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 d47f504871741c890f5daf7280c13c7412cf7e2e..4c4feea30c50c09813c157a918fb3e8ab834bf45 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -2643,43 +2643,41 @@ InputHandler::ScrollStatus LayerTreeHostImpl::ScrollBegin(
   scroll_status.main_thread_scrolling_reasons =
       MainThreadScrollingReason::kNotScrollingOnMain;
   TRACE_EVENT0("cc", "LayerTreeHostImpl::ScrollBegin");
-
+  bool scroll_on_main_thread = false;
+  LayerImpl* scrolling_layer_impl;
   // On Mac a scroll begin with |inertial_phase| = true happens to handle a
   // fling.
-  if (scroll_state->is_in_inertial_phase())
-    return FlingScrollBegin();
-
-  ClearCurrentlyScrollingLayer();
-
-  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 (scroll_state->is_in_inertial_phase()) {
+    scrolling_layer_impl = CurrentlyScrollingLayer();
+  } else {
+    ClearCurrentlyScrollingLayer();
 
-  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::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;
+      }
     }
-  }
-
-  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);
+    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);
@@ -3178,9 +3176,8 @@ void LayerTreeHostImpl::ScrollEnd(ScrollState* scroll_state) {
   DistributeScrollDelta(scroll_state);
   top_controls_manager_->ScrollEnd();
 
-  if (scroll_state->is_in_inertial_phase()) {
+  if (!scroll_state->data()->fling_might_happen_next) {
     // 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();
   }
 }