Made layout viewport scroll updates from compositor work like ordinary layers.

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 244 matching lines @@
         continue;
 
       if (scroll_delta != scroll_info.scrolls[i].scroll_delta) {
         return ::testing::AssertionFailure()
                << "Expected " << scroll_delta.ToString() << ", not "
                << scroll_info.scrolls[i].scroll_delta.ToString();
       }
       times_encountered++;
     }
 
+    if (id == scroll_info.inner_viewport_scroll.layer_id) {
+      if (scroll_delta != scroll_info.inner_viewport_scroll.scroll_delta) {
+        return ::testing::AssertionFailure()
+               << "Expected " << scroll_delta.ToString() << ", not "
+               << scroll_info.inner_viewport_scroll.scroll_delta.ToString();
+      }
+      times_encountered++;
+    }
+
     if (times_encountered != 1)
       return ::testing::AssertionFailure() << "No layer found with id " << id;
     return ::testing::AssertionSuccess();
   }
 
   static void ExpectNone(const ScrollAndScaleSet& scroll_info, int id) {
     int times_encountered = 0;
 
     for (size_t i = 0; i < scroll_info.scrolls.size(); ++i) {
       if (scroll_info.scrolls[i].layer_id != id)
@@ skipping 10771 matching lines @@
 
   // Re-initialize with a software output surface.
   output_surface_ = FakeOutputSurface::CreateSoftware(
       base::WrapUnique(new SoftwareOutputDevice));
   host_impl_->InitializeRenderer(output_surface_.get());
   EXPECT_FALSE(host_impl_->use_gpu_rasterization());
 }
 
 }  // namespace
 }  // namespace cc