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

cc/surfaces/local_frame_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_LOCAL_FRAME_ID_H_
 #define CC_SURFACES_LOCAL_FRAME_ID_H_
 
 #include <inttypes.h>
 #include <tuple>
 
 #include "base/hash.h"
 #include "base/strings/stringprintf.h"
 
 namespace cc {
 
 class LocalFrameId {
  public:
   constexpr LocalFrameId() : local_id_(0), nonce_(0) {}
 
   constexpr LocalFrameId(const LocalFrameId& other)
       : local_id_(other.local_id_), nonce_(other.nonce_) {}
 
   constexpr LocalFrameId(uint32_t local_id, uint64_t nonce)
       : local_id_(local_id), nonce_(nonce) {}
 
+  constexpr bool is_valid() const { return local_id_ != 0; }

[Fady Samuel, 2016/10/20 12:15:36]

I disagree with this. is_valid() means local_id_ != 0 and nonce_ != 0;

[Alex Z., 2016/11/08 21:38:19]

Done.

+
   constexpr bool is_null() const { return local_id_ == 0 && nonce_ == 0; }

[Fady Samuel, 2016/10/20 12:15:36]

Ideally, I'd like to get rid of is_null() because I worry that that could be
misused.

[Alex Z., 2016/11/08 21:38:19]

Done.

 
   constexpr uint32_t local_id() const { return local_id_; }
 
   constexpr uint64_t nonce() const { return nonce_; }
 
   bool operator==(const LocalFrameId& other) const {
     return local_id_ == other.local_id_ && nonce_ == other.nonce_;
   }
 
   bool operator!=(const LocalFrameId& other) const { return !(*this == other); }
@@ skipping 15 matching lines @@
   uint64_t nonce_;
 };
 
 struct LocalFrameIdHash {
   size_t operator()(const LocalFrameId& key) const { return key.hash(); }
 };
 
 }  // namespace cc
 
 #endif  // CC_SURFACES_LOCAL_FRAME_ID_H_