Implement service-side surface synchronization

cc/surfaces/local_surface_id.h

 // Copyright 2017 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_SURFACE_ID_H_
 #define CC_SURFACES_LOCAL_SURFACE_ID_H_
 
 #include <inttypes.h>
 
 #include <iosfwd>
@@ skipping 35 matching lines @@
   bool operator!=(const LocalSurfaceId& other) const {
     return !(*this == other);
   }
 
   bool operator<(const LocalSurfaceId& other) const {
     return std::tie(local_id_, nonce_) <
            std::tie(other.local_id_, other.nonce_);
   }
 
   size_t hash() const {
+    DCHECK(is_valid()) << ToString();
     return base::HashInts(
         local_id_, static_cast<uint64_t>(base::UnguessableTokenHash()(nonce_)));
   }
 
   std::string ToString() const;
 
  private:
   friend struct mojo::StructTraits<mojom::LocalSurfaceIdDataView,
                                    LocalSurfaceId>;
 
   uint32_t local_id_;
   base::UnguessableToken nonce_;
 };
 
 std::ostream& operator<<(std::ostream& out,
                          const LocalSurfaceId& local_surface_id);
 
 struct LocalSurfaceIdHash {
   size_t operator()(const LocalSurfaceId& key) const { return key.hash(); }
 };
 
 }  // namespace cc
 
 #endif  // CC_SURFACES_LOCAL_SURFACE_ID_H_