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

Source/modules/serviceworkers/ServiceWorkerClient.h

Index: Source/modules/serviceworkers/ServiceWorkerClient.h
diff --git a/Source/modules/serviceworkers/ServiceWorkerClient.h b/Source/modules/serviceworkers/ServiceWorkerClient.h
index 938fa4cc7fcee01bf2e32dbeb2b618378253d7e3..b1d96c3d1b0ee786aec80b46145e144fddca80db 100644
--- a/Source/modules/serviceworkers/ServiceWorkerClient.h
+++ b/Source/modules/serviceworkers/ServiceWorkerClient.h
@@ -5,6 +5,7 @@
 #ifndef ServiceWorkerClient_h
 #define ServiceWorkerClient_h
 
+#include "bindings/core/v8/ScriptPromise.h"
 #include "bindings/core/v8/ScriptWrappable.h"
 #include "bindings/core/v8/SerializedScriptValue.h"
 #include "platform/heap/Handle.h"
@@ -12,6 +13,9 @@
 
 namespace blink {
 
+class ExecutionContext;
+class ScriptState;
+
 class ServiceWorkerClient final : public GarbageCollected<ServiceWorkerClient>, public ScriptWrappable {
     DEFINE_WRAPPERTYPEINFO();
 public:
@@ -19,6 +23,7 @@ public:
 
     // ServiceWorkerClient.idl
     void postMessage(ExecutionContext*, PassRefPtr<SerializedScriptValue> message, const MessagePortArray*, ExceptionState&);
+    ScriptPromise focus(ScriptState*);
 
     void trace(Visitor*) { }