Worker: Add comments about thread restriction to WorkerLoaderProxy

third_party/WebKit/Source/core/workers/WorkerLoaderProxy.h

Index: third_party/WebKit/Source/core/workers/WorkerLoaderProxy.h
diff --git a/third_party/WebKit/Source/core/workers/WorkerLoaderProxy.h b/third_party/WebKit/Source/core/workers/WorkerLoaderProxy.h
index 5951d8b3ac153689a3d84c96e9f2e7041965d52f..770719fe2b78f6f1ea953bd73d5768a7a0f5ffa8 100644
--- a/third_party/WebKit/Source/core/workers/WorkerLoaderProxy.h
+++ b/third_party/WebKit/Source/core/workers/WorkerLoaderProxy.h
@@ -62,11 +62,12 @@ class CORE_EXPORT WorkerLoaderProxyProvider {
   virtual ~WorkerLoaderProxyProvider() {}
 
   // Posts a task to the thread which runs the loading code (normally, the main
-  // thread).
+  // thread). This must be called from a worker thread.
   virtual void postTaskToLoader(const WebTraceLocation&,
                                 std::unique_ptr<ExecutionContextTask>) = 0;
 
-  // Posts callbacks from loading code to the WorkerGlobalScope.
+  // Posts callbacks from loading code to the WorkerGlobalScope. This must be
+  // called from the main thread.
   virtual void postTaskToWorkerGlobalScope(
       const WebTraceLocation&,
       std::unique_ptr<WTF::CrossThreadClosure>) = 0;
@@ -82,14 +83,17 @@ class CORE_EXPORT WorkerLoaderProxy final
 
   ~WorkerLoaderProxy();
 
+  // This must be called from a worker thread.
   void postTaskToLoader(const WebTraceLocation&,
                         std::unique_ptr<ExecutionContextTask>);
+
+  // This must be called from the main thread.
   void postTaskToWorkerGlobalScope(const WebTraceLocation&,
                                    std::unique_ptr<WTF::CrossThreadClosure>);
 
   // Notification from the provider that it can no longer be accessed. An
   // implementation of WorkerLoaderProxyProvider is required to call
-  // detachProvider() when finalizing.
+  // detachProvider() when finalizing. This must be called from the main thread.
   void detachProvider(WorkerLoaderProxyProvider*);
 
  private: