[POC-WIP] Link window focus tokens with ExecutionContext.

public/web/WebServiceWorkerContextClient.h

Index: public/web/WebServiceWorkerContextClient.h
diff --git a/public/web/WebServiceWorkerContextClient.h b/public/web/WebServiceWorkerContextClient.h
index 00823667d11aef478ed621749ebc5a142f87351d..abd86580a68839ae1cecba86a2eb82e32d115488 100644
--- a/public/web/WebServiceWorkerContextClient.h
+++ b/public/web/WebServiceWorkerContextClient.h
@@ -33,6 +33,7 @@
 
 #include "WebWorkerPermissionClientProxy.h"
 #include "public/platform/WebMessagePortChannel.h"
+#include "public/platform/WebServiceWorkerClientFocusCallback.h"
 #include "public/platform/WebServiceWorkerClientsInfo.h"
 #include "public/platform/WebServiceWorkerEventResult.h"
 #include "public/platform/WebServiceWorkerSkipWaitingCallbacks.h"
@@ -154,6 +155,17 @@ public:
     // Ownership of the passed callbacks is transferred to the callee, callee
     // should delete the callbacks after run.
     virtual void skipWaiting(WebServiceWorkerSkipWaitingCallbacks*) { BLINK_ASSERT_NOT_REACHED(); }
+
+    // Ownership of the passed callbacks is transferred to the callee, callee
+    // should delete the callback after calling either onSuccess or onError.
+    virtual void focus(int clientID, WebServiceWorkerClientFocusCallback* callback)
+    {
+        // FIXME: call BLINK_ASSERT_NOT_REACHED() when Chromium implementation
+        // is present. https://crbug.com/437149
+        bool result = true;
+        callback->onSuccess(&result);
+        delete callback;
+    }
 };
 
 } // namespace blink