Use the tonic namespace for tonic + resulting build fixes

tonic/dart_string.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_STRING_H_
 #define SKY_ENGINE_TONIC_DART_STRING_H_
 
 #include "base/logging.h"
 #include "dart/runtime/include/dart_api.h"
 #include "sky/engine/wtf/text/WTFString.h"
 
-namespace blink {
+namespace tonic {
 
 Dart_Handle CreateDartString(StringImpl* string_impl);
 String ExternalizeDartString(Dart_Handle handle);
 
-}  // namespace blink
+}  // namespace tonic
 
 #endif  // SKY_ENGINE_TONIC_DART_STRING_H_