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

cc/surfaces/frame_sink_id.h

 // Copyright 2016 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.
 
 #ifndef CC_SURFACES_FRAME_SINK_ID_H_
 #define CC_SURFACES_FRAME_SINK_ID_H_
 
 #include <tuple>
 
 #include "base/format_macros.h"
 #include "base/hash.h"
 #include "base/strings/stringprintf.h"
 
 namespace cc {
 
 class FrameSinkId {
  public:
   constexpr FrameSinkId() : client_id_(0), sink_id_(0) {}
 
   constexpr FrameSinkId(const FrameSinkId& other)
       : client_id_(other.client_id_), sink_id_(other.sink_id_) {}
 
   constexpr FrameSinkId(uint32_t client_id, uint32_t sink_id)
       : client_id_(client_id), sink_id_(sink_id) {}
 
+  constexpr bool is_valid() const { return client_id_ != 0 || sink_id_ != 0; }
+
   constexpr bool is_null() const { return client_id_ == 0 && sink_id_ == 0; }
 
   constexpr uint32_t client_id() const { return client_id_; }
 
   constexpr uint32_t sink_id() const { return sink_id_; }
 
   bool operator==(const FrameSinkId& other) const {
     return client_id_ == other.client_id_ && sink_id_ == other.sink_id_;
   }
 
@@ skipping 15 matching lines @@
   uint32_t sink_id_;
 };
 
 struct FrameSinkIdHash {
   size_t operator()(const FrameSinkId& key) const { return key.hash(); }
 };
 
 }  // namespace cc
 
 #endif  // CC_SURFACES_FRAME_SINK_ID_H_