Use the tonic namespace for tonic + resulting build fixes

tonic/dart_gc_visitor.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_GC_VISITOR_H_
 #define SKY_ENGINE_TONIC_DART_GC_VISITOR_H_
 
 #include "base/logging.h"
 #include "dart/runtime/include/dart_api.h"
 
-namespace blink {
+namespace tonic {
 class DartGCContext;
 
 class DartGCVisitor {
  public:
   explicit DartGCVisitor(DartGCContext* context);
   ~DartGCVisitor();
 
   bool have_found_set() const {
     return !!current_set_;
   }
 
   Dart_WeakReferenceSet current_set() const {
     DCHECK(have_found_set());
     return current_set_;
   }
 
   void AddToSetForRoot(const void* root, Dart_WeakPersistentHandle handle);
 
  private:
   DartGCContext* context_;
   Dart_WeakReferenceSet current_set_;
 
   DISALLOW_COPY_AND_ASSIGN(DartGCVisitor);
 };
 
-}  // namespace blink
+}  // namespace tonic
 
 #endif  // SKY_ENGINE_TONIC_DART_GC_VISITOR_H_