Replaced is_null() with is_valid in SurfaceId and related classes.

ui/compositor/compositor.cc

 // Copyright (c) 2012 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 "ui/compositor/compositor.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <deque>
@@ skipping 216 matching lines @@
     host_->GetLayerTree()->animation_host()->RemoveAnimationTimeline(
         animation_timeline_.get());
 
   // Stop all outstanding draws before telling the ContextFactory to tear
   // down any contexts that the |host_| may rely upon.
   host_.reset();
 
   context_factory_->RemoveCompositor(this);
   auto* manager = context_factory_->GetSurfaceManager();
   for (auto& client : child_frame_sinks_) {
-    DCHECK(!client.is_null());
+    DCHECK(client.is_valid());
     manager->UnregisterFrameSinkHierarchy(frame_sink_id_, client);
   }
   manager->InvalidateFrameSinkId(frame_sink_id_);
 }
 
 void Compositor::AddFrameSink(const cc::FrameSinkId& frame_sink_id) {
   context_factory_->GetSurfaceManager()->RegisterFrameSinkHierarchy(
       frame_sink_id_, frame_sink_id);
   child_frame_sinks_.insert(frame_sink_id);
 }
 
 void Compositor::RemoveFrameSink(const cc::FrameSinkId& frame_sink_id) {
   auto it = child_frame_sinks_.find(frame_sink_id);
   DCHECK(it != child_frame_sinks_.end());
-  DCHECK(!it->is_null());
+  DCHECK(it->is_valid());
   context_factory_->GetSurfaceManager()->UnregisterFrameSinkHierarchy(
       frame_sink_id_, *it);
   child_frame_sinks_.erase(it);
 }
 
 void Compositor::SetCompositorFrameSink(
     std::unique_ptr<cc::CompositorFrameSink> compositor_frame_sink) {
   compositor_frame_sink_requested_ = false;
   host_->SetCompositorFrameSink(std::move(compositor_frame_sink));
   // Display properties are reset when the output surface is lost, so update it
@@ skipping 277 matching lines @@
   for (auto& observer : observer_list_)
     observer.OnCompositingLockStateChanged(this);
 }
 
 void Compositor::CancelCompositorLock() {
   if (compositor_lock_)
     compositor_lock_->CancelLock();
 }
 
 }  // namespace ui