[Android] Avoid setting update_draw_properties.

cc/layers/layer_impl.cc

Index: cc/layers/layer_impl.cc
diff --git a/cc/layers/layer_impl.cc b/cc/layers/layer_impl.cc
index 5c9eada05addd2181ad8ea1a5d9a46a83d15bff2..d833874b37b90a531e10ce763b0229bae348da09 100644
--- a/cc/layers/layer_impl.cc
+++ b/cc/layers/layer_impl.cc
@@ -1295,23 +1295,26 @@ void LayerImpl::SetScrollbarPosition(ScrollbarLayerImplBase* scrollbar_layer,
     scrollbar_needs_animation |=
         scrollbar_layer->SetVisibleToTotalLengthRatio(visible_ratio);
   }
-
-  layer_tree_impl()->set_needs_update_draw_properties();
-  // TODO(wjmaclean) The scrollbar animator for the pinch-zoom scrollbars should
-  // activate for every scroll on the main frame, not just the scrolls that move
-  // the pinch virtual viewport (i.e. trigger from either inner or outer
-  // viewport).
-  if (scrollbar_animation_controller_ && scrollbar_needs_animation) {
-    // When both non-overlay and overlay scrollbars are both present, don't
-    // animate the overlay scrollbars when page scale factor is at the min.
-    // Non-overlay scrollbars also shouldn't trigger animations.
-    bool is_animatable_scrollbar =
-        scrollbar_layer->is_overlay_scrollbar() &&
-        ((layer_tree_impl()->total_page_scale_factor() >
-          layer_tree_impl()->min_page_scale_factor()) ||
-         !layer_tree_impl()->settings().use_pinch_zoom_scrollbars);
-    if (is_animatable_scrollbar)
-      scrollbar_animation_controller_->DidScrollUpdate();
+  if (scrollbar_needs_animation) {
+    layer_tree_impl()->set_needs_update_draw_properties();
+    // TODO(wjmaclean) The scrollbar animator for the pinch-zoom scrollbars

[wjmaclean, 2014/09/23 14:30:13]

nit: please reformat this comment

[MuVen, 2014/09/23 14:44:08]

Done.

+    // should
+    // activate for every scroll on the main frame, not just the scrolls that
+    // move
+    // the pinch virtual viewport (i.e. trigger from either inner or outer
+    // viewport).
+    if (scrollbar_animation_controller_) {
+      // When both non-overlay and overlay scrollbars are both present, don't
+      // animate the overlay scrollbars when page scale factor is at the min.
+      // Non-overlay scrollbars also shouldn't trigger animations.
+      bool is_animatable_scrollbar =
+          scrollbar_layer->is_overlay_scrollbar() &&
+          ((layer_tree_impl()->total_page_scale_factor() >
+            layer_tree_impl()->min_page_scale_factor()) ||
+           !layer_tree_impl()->settings().use_pinch_zoom_scrollbars);
+      if (is_animatable_scrollbar)
+        scrollbar_animation_controller_->DidScrollUpdate();
+    }
   }
 }