Call SAC::DidScrollUpdate only for compositor-triggered scrolls.

cc/trees/layer_tree_impl.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/trees/layer_tree_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 224 matching lines @@
     return;
 
   gfx::ScrollOffset current_offset = scroll_layer->CurrentScrollOffset();
   if (IsViewportLayerId(scroll_layer_id)) {
     current_offset += InnerViewportScrollLayer()->CurrentScrollOffset();
     if (OuterViewportContainerLayer())
       clip_size.SetToMin(OuterViewportContainerLayer()->BoundsForScrolling());
     clip_size.Scale(1 / current_page_scale_factor());
   }
 
-  bool scrollbar_needs_animation = false;
-  bool clip_layer_size_did_change = false;
-  bool scroll_layer_size_did_change = false;
   bool y_offset_did_change = false;
   for (auto* scrollbar : ScrollbarsFor(scroll_layer->element_id())) {
     if (scrollbar->orientation() == HORIZONTAL) {
-      scrollbar_needs_animation |= scrollbar->SetCurrentPos(current_offset.x());
-      clip_layer_size_did_change |=
-          scrollbar->SetClipLayerLength(clip_size.width());
-      scroll_layer_size_did_change |=
-          scrollbar->SetScrollLayerLength(scroll_size.width());
+      scrollbar->SetCurrentPos(current_offset.x());
+      scrollbar->SetClipLayerLength(clip_size.width());
+      scrollbar->SetScrollLayerLength(scroll_size.width());
     } else {
-      scrollbar_needs_animation |= y_offset_did_change |=
-          scrollbar->SetCurrentPos(current_offset.y());
-      clip_layer_size_did_change |=
-          scrollbar->SetClipLayerLength(clip_size.height());
-      scroll_layer_size_did_change |=
-          scrollbar->SetScrollLayerLength(scroll_size.height());
+      y_offset_did_change = scrollbar->SetCurrentPos(current_offset.y());
+      scrollbar->SetClipLayerLength(clip_size.height());
+      scrollbar->SetScrollLayerLength(scroll_size.height());
     }
-    scrollbar_needs_animation |=
-        scrollbar->SetVerticalAdjust(clip_layer->bounds_delta().y());
+    scrollbar->SetVerticalAdjust(clip_layer->bounds_delta().y());
   }
 
-  scrollbar_needs_animation |=
-      (clip_layer_size_did_change || scroll_layer_size_did_change);
-
   if (y_offset_did_change && IsViewportLayerId(scroll_layer_id))
     TRACE_COUNTER_ID1("cc", "scroll_offset_y", scroll_layer->id(),
                       current_offset.y());
-
-  if (scrollbar_needs_animation) {
-    ScrollbarAnimationController* controller =
-        layer_tree_host_impl_->ScrollbarAnimationControllerForElementId(
-            scroll_layer->element_id());
-    if (!controller)
-      return;
-
-    // TODO(chaopeng) clip_layer_size_did_change should call DidResize after
-    // crbug.com/701810 got fixed.
-    if (scroll_layer_size_did_change) {
-      controller->DidResize();
-    } else {
-      controller->DidScrollUpdate();
-    }
-  }
 }
 
 RenderSurfaceImpl* LayerTreeImpl::RootRenderSurface() const {
   return layer_list_.empty() ? nullptr : layer_list_[0]->GetRenderSurface();
 }
 
 bool LayerTreeImpl::LayerListIsEmpty() const {
   return layer_list_.empty();
 }
 
@@ skipping 658 matching lines @@
   return true;
 }
 
 void LayerTreeImpl::DidUpdatePageScale() {
   if (IsActiveTree())
     page_scale_factor()->SetCurrent(
         ClampPageScaleFactorToLimits(current_page_scale_factor()));
 
   set_needs_update_draw_properties();
   DidUpdateScrollState(inner_viewport_scroll_layer_id_);
+
+  if (IsActiveTree() && OuterViewportScrollLayer()) {

[bokan, 2017/04/25 22:56:48]

Use LTHI::ViewportMainScrollLayer rather than OuterViewportScrollLayer (it's an
alias for the outer layer but makes clear where we reference the viewport).

[skobes, 2017/04/27 00:46:31]

Done.

+    if (ScrollbarAnimationController* controller =
+            layer_tree_host_impl_->ScrollbarAnimationControllerForElementId(
+                OuterViewportScrollLayer()->element_id()))
+      controller->DidScrollUpdate();
+  }
 }
 
 void LayerTreeImpl::SetDeviceScaleFactor(float device_scale_factor) {
   if (device_scale_factor == device_scale_factor_)
     return;
   device_scale_factor_ = device_scale_factor;
 
   set_needs_update_draw_properties();
   if (IsActiveTree())
     layer_tree_host_impl_->SetFullViewportDamage();
@@ skipping 1200 matching lines @@
 
 void LayerTreeImpl::ResetAllChangeTracking() {
   layers_that_should_push_properties_.clear();
   // Iterate over all layers, including masks.
   for (auto& layer : *layers_)
     layer->ResetChangeTracking();
   property_trees_.ResetAllChangeTracking();
 }
 
 }  // namespace cc