Implement the infrastructure of creating WorkerFetchContext in worker global scope.

third_party/WebKit/public/platform/Platform.h

Index: third_party/WebKit/public/platform/Platform.h
diff --git a/third_party/WebKit/public/platform/Platform.h b/third_party/WebKit/public/platform/Platform.h
index eab1ca5647cb791538ec8b33fef4eaba3584bd08..bbe830726e0594f5288bd6b068d98f95a01978c5 100644
--- a/third_party/WebKit/public/platform/Platform.h
+++ b/third_party/WebKit/public/platform/Platform.h
@@ -55,6 +55,7 @@
 #include "WebString.h"
 #include "WebURLError.h"
 #include "WebVector.h"
+#include "WebWorkerFetchContext.h"
 #include "base/metrics/user_metrics_action.h"
 #include "cc/resources/shared_bitmap.h"
 #include "cc/surfaces/frame_sink_id.h"
@@ -359,6 +360,12 @@ class BLINK_PLATFORM_EXPORT Platform {
     return WebURLError();
   }
 
+  // Returns a new WebWorkerFetchContext for a dedicated (or shared) worker.
+  // Returns nullptr if off-main-thread-fetch is disabled.
+  virtual std::unique_ptr<WebWorkerFetchContext> CreateWorkerFetchContext() {
+    return nullptr;
+  }
+
   // Plugins -------------------------------------------------------------
 
   // If refresh is true, then cached information should not be used to