Remove some more WTF usage

sky/engine/tonic/dart_library_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_library_loader.h"
 
 #include "base/callback.h"
 #include "base/trace_event/trace_event.h"
 #include "mojo/common/data_pipe_drainer.h"
 #include "sky/engine/tonic/dart_api_scope.h"
 #include "sky/engine/tonic/dart_converter.h"
 #include "sky/engine/tonic/dart_dependency_catcher.h"
 #include "sky/engine/tonic/dart_error.h"
 #include "sky/engine/tonic/dart_isolate_scope.h"
 #include "sky/engine/tonic/dart_library_provider.h"
 #include "sky/engine/tonic/dart_state.h"
-#include "sky/engine/wtf/MainThread.h"
 
 using mojo::common::DataPipeDrainer;
 
 namespace blink {
 
 namespace {
 
 // Helper to erase a T* from a container of std::unique_ptr<T>s.
 template<typename T, typename C>
 void EraseUniquePtr(C& container, T* item) {
@@ skipping 165 matching lines @@
 }
 
 Dart_Handle DartLibraryLoader::HandleLibraryTag(Dart_LibraryTag tag,
                                                 Dart_Handle library,
                                                 Dart_Handle url) {
   DCHECK(Dart_IsLibrary(library));
   DCHECK(Dart_IsString(url));
   if (tag == Dart_kCanonicalizeUrl)
     return DartState::Current()->library_loader().CanonicalizeURL(library, url);
   if (tag == Dart_kImportTag) {
-    CHECK(WTF::isMainThread());
     return DartState::Current()->library_loader().Import(library, url);
   }
   if (tag == Dart_kSourceTag) {
-    CHECK(WTF::isMainThread());
     return DartState::Current()->library_loader().Source(library, url);
   }
   DCHECK(false);
   return Dart_NewApiError("Unknown library tag.");
 }
 
 void DartLibraryLoader::WaitForDependencies(
     const std::unordered_set<DartDependency*>& dependencies,
     const base::Closure& callback) {
   if (dependencies.empty())
@@ skipping 81 matching lines @@
 
   WatcherSignaler watcher_signaler(*this, job);
 
   LOG(ERROR) << "Library Load failed: " << job->name();
   // TODO(eseidel): Call Dart_LibraryHandleError in the SourceJob case?
 
   EraseUniquePtr<Job>(jobs_, job);
 }
 
 }  // namespace blink