Make scroll offset type of float in cc

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 1067 matching lines @@
   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()) {
       inner_viewport_scroll_delta += info->scrolls[i].scroll_delta;
     } else {
-      layer->SetScrollOffsetFromImplSide(layer->scroll_offset() +
-                                         info->scrolls[i].scroll_delta);
+      layer->SetScrollOffsetFromImplSide(
+          gfx::ScrollOffsetWithDelta(layer->scroll_offset(),
+                                     info->scrolls[i].scroll_delta));
     }
   }
 
   if (!inner_viewport_scroll_delta.IsZero() ||
       !outer_viewport_scroll_delta.IsZero() ||
       info->page_scale_delta != 1.f ||
       info->top_controls_delta) {
     // SetScrollOffsetFromImplSide above could have destroyed the tree,
     // so re-get this layer before doing anything to it.
 
     DCHECK(inner_viewport_scroll_layer_.get());  // We should always have this.
 
     // Preemptively apply the scroll offset and scale delta here before sending
     // it to the client.  If the client comes back and sets it to the same
     // value, then the layer can early out without needing a full commit.
     inner_viewport_scroll_layer_->SetScrollOffsetFromImplSide(
-        inner_viewport_scroll_layer_->scroll_offset() +
-        inner_viewport_scroll_delta);
+        gfx::ScrollOffsetWithDelta(
+            inner_viewport_scroll_layer_->scroll_offset(),
+            inner_viewport_scroll_delta));
     if (outer_viewport_scroll_layer_.get()) {
       outer_viewport_scroll_layer_->SetScrollOffsetFromImplSide(
-          outer_viewport_scroll_layer_->scroll_offset() +
-          outer_viewport_scroll_delta);
+          gfx::ScrollOffsetWithDelta(
+              outer_viewport_scroll_layer_->scroll_offset(),
+              outer_viewport_scroll_delta));
     }
 
     ApplyPageScaleDeltaFromImplSide(info->page_scale_delta);
     if (!outer_viewport_scroll_layer_.get()) {
       client_->ApplyViewportDeltas(
           inner_viewport_scroll_delta + outer_viewport_scroll_delta,
           info->page_scale_delta,
           info->top_controls_delta);
     } else {
       client_->ApplyViewportDeltas(
@@ skipping 209 matching lines @@
   swap_promise_list_.push_back(swap_promise.Pass());
 }
 
 void LayerTreeHost::BreakSwapPromises(SwapPromise::DidNotSwapReason reason) {
   for (size_t i = 0; i < swap_promise_list_.size(); i++)
     swap_promise_list_[i]->DidNotSwap(reason);
   swap_promise_list_.clear();
 }
 
 }  // namespace cc