Use the tonic namespace for tonic + resulting build fixes

tonic/dart_isolate_scope.h

 // Copyright 2015 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 SKY_ENGINE_TONIC_DART_ISOLATE_SCOPE_H_
 #define SKY_ENGINE_TONIC_DART_ISOLATE_SCOPE_H_
 
 #include "base/logging.h"
 #include "dart/runtime/include/dart_api.h"
 
-namespace blink {
+namespace tonic {
 
 // DartIsolateScope is a helper class for entering and exiting a given isolate.
 class DartIsolateScope {
  public:
   explicit DartIsolateScope(Dart_Isolate isolate);
   ~DartIsolateScope();
 
  private:
   Dart_Isolate isolate_;
   Dart_Isolate previous_;
 
   DISALLOW_COPY_AND_ASSIGN(DartIsolateScope);
 };
 
-}  // namespace blink
+}  // namespace tonic
 
 #endif  // SKY_ENGINE_TONIC_DART_ISOLATE_SCOPE_H_