Implement the infrastructure of creating WorkerFetchContext in worker global scope.

third_party/WebKit/public/web/WebSharedWorkerClient.h

Index: third_party/WebKit/public/web/WebSharedWorkerClient.h
diff --git a/third_party/WebKit/public/web/WebSharedWorkerClient.h b/third_party/WebKit/public/web/WebSharedWorkerClient.h
index 46f8cf1d1aa872e73235f5f04264b46c42685a57..93ac90f52e40bf3689566bbf2b9fda00e4566d34 100644
--- a/third_party/WebKit/public/web/WebSharedWorkerClient.h
+++ b/third_party/WebKit/public/web/WebSharedWorkerClient.h
@@ -32,6 +32,7 @@
 #define WebSharedWorkerClient_h
 
 #include "public/platform/WebMessagePortChannel.h"
+#include "public/platform/WebWorkerFetchContext.h"
 #include "public/web/WebDevToolsAgentClient.h"
 
 namespace blink {
@@ -93,6 +94,14 @@ class WebSharedWorkerClient {
   CreateDevToolsMessageLoop() {
     return nullptr;
   }
+
+  // Returns a new WebWorkerFetchContext for the shared worker. Ownership of the
+  // returned object is transferred to the caller. This is used only when
+  // off-main-thread-fetch is enabled.
+  virtual std::unique_ptr<WebWorkerFetchContext> CreateWorkerFetchContext(
+      WebServiceWorkerNetworkProvider*) {
+    return nullptr;
+  }
 };
 
 }  // namespace blink