Remove some more WTF usage

sky/engine/tonic/dart_snapshot_loader.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 "sky/engine/tonic/dart_snapshot_loader.h"
 
 #include "base/callback.h"
 #include "base/trace_event/trace_event.h"
 #include "sky/engine/tonic/dart_api_scope.h"
 #include "sky/engine/tonic/dart_converter.h"
 #include "sky/engine/tonic/dart_error.h"
 #include "sky/engine/tonic/dart_isolate_scope.h"
-#include "sky/engine/wtf/MainThread.h"
 
 using mojo::common::DataPipeDrainer;
 
 namespace blink {
 
 DartSnapshotLoader::DartSnapshotLoader(DartState* dart_state)
     : dart_state_(dart_state->GetWeakPtr()) {
 }
 
 DartSnapshotLoader::~DartSnapshotLoader() {
@@ skipping 20 matching lines @@
     DartIsolateScope scope(dart_state_->isolate());
     DartApiScope api_scope;
 
     LogIfError(Dart_LoadScriptFromSnapshot(buffer_.data(), buffer_.size()));
   }
 
   callback_.Run();
 }
 
 }  // namespace blink