cc: Be less aggressive about scheduling for scroll handlers

cc/trees/thread_proxy.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/thread_proxy.h"
 
 #include <algorithm>
 #include <string>
 
 #include "base/auto_reset.h"
@@ skipping 1316 matching lines @@
     *main_frame_will_happen = false;
   }
   completion->Signal();
 }
 
 void ThreadProxy::RenewTreePriority() {
   DCHECK(IsImplThread());
   bool smoothness_takes_priority =
       impl().layer_tree_host_impl->pinch_gesture_active() ||
       impl().layer_tree_host_impl->page_scale_animation_active() ||
-      (impl().layer_tree_host_impl->IsCurrentlyScrolling() &&
-       !impl().layer_tree_host_impl->scroll_affects_scroll_handler());
+      impl().layer_tree_host_impl->IsCurrentlyScrolling();
 
   // Schedule expiration if smoothness currently takes priority.
   if (smoothness_takes_priority)
     impl().smoothness_priority_expiration_notifier.Schedule();
 
   // We use the same priority for both trees by default.
   TreePriority priority = SAME_PRIORITY_FOR_BOTH_TREES;
 
   // Smoothness takes priority if we have an expiration for it scheduled.
   if (impl().smoothness_priority_expiration_notifier.HasPendingNotification())
     priority = SMOOTHNESS_TAKES_PRIORITY;
 
   // New content always takes priority when the active tree has
   // evicted resources or there is an invalid viewport size.
   if (impl().layer_tree_host_impl->active_tree()->ContentsTexturesPurged() ||
       impl().layer_tree_host_impl->active_tree()->ViewportSizeInvalid() ||
       impl().layer_tree_host_impl->EvictedUIResourcesExist() ||
       impl().input_throttled_until_commit) {
     // Once we enter NEW_CONTENTS_TAKES_PRIORITY mode, visible tiles on active
     // tree might be freed. We need to set RequiresHighResToDraw to ensure that
     // high res tiles will be required to activate pending tree.
     impl().layer_tree_host_impl->active_tree()->SetRequiresHighResToDraw();
     priority = NEW_CONTENT_TAKES_PRIORITY;
   }
 
   impl().layer_tree_host_impl->SetTreePriority(priority);
-  impl().scheduler->SetSmoothnessTakesPriority(priority ==
-                                               SMOOTHNESS_TAKES_PRIORITY);
+
+  // Only put the scheduler in impl latency prioritization mode if we don't
+  // have a scroll listener. This gives the scroll listener a better chance of
+  // handling scroll updates within the same frame. The tree itself is still
+  // kept in prefer smoothness mode to allow checkerboarding.
+  impl().scheduler->SetImplLatencyTakesPriority(
+      priority == SMOOTHNESS_TAKES_PRIORITY &&
+      !impl().layer_tree_host_impl->scroll_affects_scroll_handler());
 
   // Notify the the client of this compositor via the output surface.
   // TODO(epenner): Route this to compositor-thread instead of output-surface
   // after GTFO refactor of compositor-thread (http://crbug/170828).
   if (impl().layer_tree_host_impl->output_surface()) {
     impl()
         .layer_tree_host_impl->output_surface()
         ->UpdateSmoothnessTakesPriority(priority == SMOOTHNESS_TAKES_PRIORITY);
   }
 }
@@ skipping 20 matching lines @@
 
   impl().timing_history.DidActivateSyncTree();
 }
 
 void ThreadProxy::DidManageTiles() {
   DCHECK(IsImplThread());
   impl().scheduler->DidManageTiles();
 }
 
 }  // namespace cc