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

cc/surfaces/surface_id.h

 // Copyright 2014 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_SURFACE_ID_H_
 #define CC_SURFACES_SURFACE_ID_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 23 matching lines @@
   // that uniquely identifies a sequential set of frames of the same size and
   // device scale factor.
   // A |nonce| is a cryptographically secure unguessable token that makes it
   // impossible for an unprivileged frame source to embed another frame source
   // without being explicitly given the surface ID of that frame source from a
   // privileged process.
   SurfaceId(const FrameSinkId& frame_sink_id,
             const LocalFrameId& local_frame_id)
       : frame_sink_id_(frame_sink_id), local_frame_id_(local_frame_id) {}
 
+  bool is_valid() const {
+    return frame_sink_id_.is_valid() && local_frame_id_.is_valid();
+  }
+
   bool is_null() const {
     return frame_sink_id_.is_null() && local_frame_id_.is_null();
   }
 
   size_t hash() const {
     return base::HashInts(static_cast<uint64_t>(frame_sink_id_.hash()),
                           static_cast<uint64_t>(local_frame_id_.hash()));
   }
 
   const FrameSinkId& frame_sink_id() const { return frame_sink_id_; }
@@ skipping 24 matching lines @@
   LocalFrameId local_frame_id_;
 };
 
 struct SurfaceIdHash {
   size_t operator()(const SurfaceId& key) const { return key.hash(); }
 };
 
 }  // namespace cc
 
 #endif  // CC_SURFACES_SURFACE_ID_H_