Update from https://crrev.com/315085

cc/trees/layer_tree_host.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.h"
 
 #include <algorithm>
 #include <stack>
 #include <string>
 
@@ skipping 25 matching lines @@
 #include "cc/scheduler/begin_frame_source.h"
 #include "cc/trees/layer_tree_host_client.h"
 #include "cc/trees/layer_tree_host_common.h"
 #include "cc/trees/layer_tree_host_impl.h"
 #include "cc/trees/layer_tree_impl.h"
 #include "cc/trees/occlusion_tracker.h"
 #include "cc/trees/single_thread_proxy.h"
 #include "cc/trees/thread_proxy.h"
 #include "cc/trees/tree_synchronizer.h"
 #include "ui/gfx/geometry/size_conversions.h"
+#include "ui/gfx/geometry/vector2d_conversions.h"
 
 namespace {
 static base::StaticAtomicSequenceNumber s_layer_tree_host_sequence_number;
 }
 
 namespace cc {
 
 RendererCapabilities::RendererCapabilities(ResourceFormat best_texture_format,
                                            bool allow_partial_texture_updates,
                                            int max_texture_size,
@@ skipping 159 matching lines @@
   layer->OnOutputSurfaceCreated();
 }
 
 void LayerTreeHost::DeleteContentsTexturesOnImplThread(
     ResourceProvider* resource_provider) {
   DCHECK(proxy_->IsImplThread());
   if (contents_texture_manager_)
     contents_texture_manager_->ClearAllMemory(resource_provider);
 }
 
+void LayerTreeHost::WillBeginMainFrame() {
+  devtools_instrumentation::WillBeginMainThreadFrame(id(),
+                                                     source_frame_number());
+  client_->WillBeginMainFrame();
+}
+
 void LayerTreeHost::DidBeginMainFrame() {
   client_->DidBeginMainFrame();
 }
 
 void LayerTreeHost::BeginMainFrame(const BeginFrameArgs& args) {
   inside_begin_main_frame_ = true;
   client_->BeginMainFrame(args);
   inside_begin_main_frame_ = false;
 }
 
@@ skipping 845 matching lines @@
   ScopedPtrVector<SwapPromise>::iterator it = info->swap_promises.begin();
   for (; it != info->swap_promises.end(); ++it) {
     scoped_ptr<SwapPromise> swap_promise(info->swap_promises.take(it));
     TRACE_EVENT_FLOW_STEP0("input",
                            "LatencyInfo.Flow",
                            TRACE_ID_DONT_MANGLE(swap_promise->TraceId()),
                            "Main thread scroll update");
     QueueSwapPromise(swap_promise.Pass());
   }
 
-  gfx::Vector2d inner_viewport_scroll_delta;
-  gfx::Vector2d outer_viewport_scroll_delta;
+  gfx::Vector2dF inner_viewport_scroll_delta;
+  gfx::Vector2dF outer_viewport_scroll_delta;
 
   if (root_layer_.get()) {
     for (size_t i = 0; i < info->scrolls.size(); ++i) {
       Layer* layer = LayerTreeHostCommon::FindLayerInSubtree(
           root_layer_.get(), info->scrolls[i].layer_id);
       if (!layer)
         continue;
       if (layer == outer_viewport_scroll_layer_.get()) {
         outer_viewport_scroll_delta += info->scrolls[i].scroll_delta;
       } else if (layer == inner_viewport_scroll_layer_.get()) {
@@ skipping 22 matching lines @@
     if (outer_viewport_scroll_layer_.get()) {
       outer_viewport_scroll_layer_->SetScrollOffsetFromImplSide(
           gfx::ScrollOffsetWithDelta(
               outer_viewport_scroll_layer_->scroll_offset(),
               outer_viewport_scroll_delta));
     }
 
     ApplyPageScaleDeltaFromImplSide(info->page_scale_delta);
     elastic_overscroll_ += info->elastic_overscroll_delta;
     if (!settings_.use_pinch_virtual_viewport) {
+      // TODO(miletus): Make sure either this code path is totally gone,
+      // or revisit the flooring here if the old pinch viewport code path
+      // is causing problems with fractional scroll offset.
       client_->ApplyViewportDeltas(
-          inner_viewport_scroll_delta + outer_viewport_scroll_delta,
-          info->page_scale_delta,
-          info->top_controls_delta);
+          gfx::ToFlooredVector2d(inner_viewport_scroll_delta +
+                                 outer_viewport_scroll_delta),
+          info->page_scale_delta, info->top_controls_delta);
     } else {
       // TODO(ccameron): pass the elastic overscroll here so that input events
       // may be translated appropriately.
       client_->ApplyViewportDeltas(
           inner_viewport_scroll_delta, outer_viewport_scroll_delta,
           info->elastic_overscroll_delta, info->page_scale_delta,
           info->top_controls_delta);
     }
   }
 }
@@ skipping 222 matching lines @@
     bool children_need_begin_frames) const {
   proxy_->SetChildrenNeedBeginFrames(children_need_begin_frames);
 }
 
 void LayerTreeHost::SendBeginFramesToChildren(
     const BeginFrameArgs& args) const {
   client_->SendBeginFramesToChildren(args);
 }
 
 }  // namespace cc