Use the tonic namespace for tonic + resulting build fixes

tonic/dart_isolate_scope.cc

 // 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.
 
 #include "tonic/dart_isolate_scope.h"
 
-namespace blink {
+namespace tonic {
 
 DartIsolateScope::DartIsolateScope(Dart_Isolate isolate) {
   isolate_ = isolate;
   previous_ = Dart_CurrentIsolate();
   if (previous_ == isolate_)
     return;
   if (previous_)
     Dart_ExitIsolate();
   Dart_EnterIsolate(isolate_);
 }
 
 DartIsolateScope::~DartIsolateScope() {
   DCHECK(Dart_CurrentIsolate() == isolate_);
   if (previous_ == isolate_)
     return;
   Dart_ExitIsolate();
   if (previous_)
     Dart_EnterIsolate(previous_);
 }
 
-}  // namespace blink
+}  // namespace tonic