Reduce composited smooth scroll latency by a frame (also fixes latency UMAs).

cc/trees/layer_tree_host_impl_unittest.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_host_impl.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <cmath>
@@ skipping 5623 matching lines @@
   EXPECT_EQ(
       InputHandler::SCROLL_ON_IMPL_THREAD,
       host_impl_->ScrollAnimated(gfx::Point(), gfx::Vector2d(0, -100)).thread);
 
   begin_frame_args.frame_time = start_time;
   begin_frame_args.sequence_number++;
   host_impl_->WillBeginImplFrame(begin_frame_args);
   host_impl_->Animate();
   host_impl_->UpdateAnimationState(true);
 
-  EXPECT_EQ(gfx::ScrollOffset(0, 30), grand_child_layer->CurrentScrollOffset());
+  // Should have started scrolling.
+  EXPECT_NE(gfx::ScrollOffset(0, 30), grand_child_layer->CurrentScrollOffset());
   host_impl_->DidFinishImplFrame();
 
   begin_frame_args.frame_time =
       start_time + base::TimeDelta::FromMilliseconds(200);
   begin_frame_args.sequence_number++;
   host_impl_->WillBeginImplFrame(begin_frame_args);
   host_impl_->Animate();
   host_impl_->UpdateAnimationState(true);
 
   EXPECT_EQ(gfx::ScrollOffset(0, 0), grand_child_layer->CurrentScrollOffset());
@@ skipping 5097 matching lines @@
   LayerImpl* scrolling_layer = host_impl_->OuterViewportScrollLayer();
   EXPECT_EQ(scrolling_layer->scroll_tree_index(),
             host_impl_->CurrentlyScrollingNode()->id);
 
   begin_frame_args.frame_time = start_time;
   begin_frame_args.sequence_number++;
   host_impl_->WillBeginImplFrame(begin_frame_args);
   host_impl_->Animate();
   host_impl_->UpdateAnimationState(true);
 
-  EXPECT_EQ(gfx::ScrollOffset(), scrolling_layer->CurrentScrollOffset());
+  EXPECT_NE(gfx::ScrollOffset(), scrolling_layer->CurrentScrollOffset());
   host_impl_->DidFinishImplFrame();
 
   begin_frame_args.frame_time =
       start_time + base::TimeDelta::FromMilliseconds(50);
   begin_frame_args.sequence_number++;
   host_impl_->WillBeginImplFrame(begin_frame_args);
   host_impl_->Animate();
   host_impl_->UpdateAnimationState(true);
 
   float y = scrolling_layer->CurrentScrollOffset().y();
@@ skipping 120 matching lines @@
 
   LayerImpl* scrolling_layer = host_impl_->OuterViewportScrollLayer();
   EXPECT_EQ(scrolling_layer->scroll_tree_index(),
             host_impl_->CurrentlyScrollingNode()->id);
 
   // First tick, animation is started.
   begin_frame_args.frame_time = start_time;
   begin_frame_args.sequence_number++;
   host_impl_->WillBeginImplFrame(begin_frame_args);
   host_impl_->UpdateAnimationState(true);
-  EXPECT_EQ(gfx::ScrollOffset(), scrolling_layer->CurrentScrollOffset());
+  EXPECT_NE(gfx::ScrollOffset(), scrolling_layer->CurrentScrollOffset());
   host_impl_->DidFinishImplFrame();
 
-  // Second tick after 50ms, animation should be half way done since
-  // the duration due to delay is 100ms.
-  begin_frame_args.frame_time =
-      start_time + base::TimeDelta::FromMilliseconds(50);
+  // Second tick after 50ms, animation should be half way done since the
+  // duration due to delay is 100ms. Subtract off the frame interval since we
+  // progress a full frame on the first tick.
+  base::TimeTicks half_way_time = start_time - begin_frame_args.interval +
+                                  base::TimeDelta::FromMilliseconds(50);
+  begin_frame_args.frame_time = half_way_time;
   begin_frame_args.sequence_number++;
   host_impl_->WillBeginImplFrame(begin_frame_args);
   host_impl_->UpdateAnimationState(true);
   EXPECT_EQ(50, scrolling_layer->CurrentScrollOffset().y());
   host_impl_->DidFinishImplFrame();
 
   // Update target.
   EXPECT_EQ(InputHandler::SCROLL_ON_IMPL_THREAD,
             host_impl_
                 ->ScrollAnimated(gfx::Point(), gfx::Vector2d(0, 100),
@@ skipping 36 matching lines @@
 
   begin_frame_args.frame_time = start_time;
   begin_frame_args.sequence_number++;
   host_impl_->WillBeginImplFrame(begin_frame_args);
   host_impl_->Animate();
   host_impl_->UpdateAnimationState(true);
 
   EXPECT_TRUE(GetImplAnimationHost()->HasAnyAnimationTargetingProperty(
       scrolling_layer->element_id(), TargetProperty::SCROLL_OFFSET));
 
-  EXPECT_EQ(gfx::ScrollOffset(), scrolling_layer->CurrentScrollOffset());
+  EXPECT_NE(gfx::ScrollOffset(), scrolling_layer->CurrentScrollOffset());
   host_impl_->DidFinishImplFrame();
 
   begin_frame_args.frame_time =
       start_time + base::TimeDelta::FromMilliseconds(50);
   begin_frame_args.sequence_number++;
   host_impl_->WillBeginImplFrame(begin_frame_args);
   host_impl_->Animate();
   host_impl_->UpdateAnimationState(true);
 
   float y = scrolling_layer->CurrentScrollOffset().y();
@@ skipping 48 matching lines @@
   LayerImpl* scrolling_layer = host_impl_->OuterViewportScrollLayer();
   EXPECT_EQ(scrolling_layer->scroll_tree_index(),
             host_impl_->CurrentlyScrollingNode()->id);
 
   begin_frame_args.frame_time = start_time;
   begin_frame_args.sequence_number++;
   host_impl_->WillBeginImplFrame(begin_frame_args);
   host_impl_->Animate();
   host_impl_->UpdateAnimationState(true);
 
-  EXPECT_EQ(gfx::ScrollOffset(), scrolling_layer->CurrentScrollOffset());
+  EXPECT_NE(gfx::ScrollOffset(), scrolling_layer->CurrentScrollOffset());
   host_impl_->DidFinishImplFrame();
 
   begin_frame_args.frame_time =
       start_time + base::TimeDelta::FromMilliseconds(50);
   begin_frame_args.sequence_number++;
   host_impl_->WillBeginImplFrame(begin_frame_args);
   host_impl_->Animate();
   host_impl_->UpdateAnimationState(true);
 
   float y = scrolling_layer->CurrentScrollOffset().y();
@@ skipping 215 matching lines @@
   LayerImpl* scrolling_layer = host_impl_->OuterViewportScrollLayer();
   EXPECT_EQ(scrolling_layer->scroll_tree_index(),
             host_impl_->CurrentlyScrollingNode()->id);
 
   begin_frame_args.frame_time = start_time;
   begin_frame_args.sequence_number++;
   host_impl_->WillBeginImplFrame(begin_frame_args);
   host_impl_->Animate();
   host_impl_->UpdateAnimationState(true);
 
-  EXPECT_EQ(gfx::ScrollOffset(), scrolling_layer->CurrentScrollOffset());
+  EXPECT_NE(gfx::ScrollOffset(), scrolling_layer->CurrentScrollOffset());
   host_impl_->DidFinishImplFrame();
 
   begin_frame_args.frame_time =
       start_time + base::TimeDelta::FromMilliseconds(50);
   begin_frame_args.sequence_number++;
   host_impl_->WillBeginImplFrame(begin_frame_args);
   host_impl_->Animate();
   host_impl_->UpdateAnimationState(true);
 
   // Should not have scrolled horizontally.
@@ skipping 1095 matching lines @@
     else
       EXPECT_FALSE(tile->HasRasterTask());
   }
   Region expected_invalidation(
       raster_source->GetRectForImage(checkerable_image->uniqueID()));
   EXPECT_EQ(expected_invalidation, *(root->GetPendingInvalidation()));
 }
 
 }  // namespace
 }  // namespace cc