[BackgroundSync] Only allow SyncManager.register to occur from main frame

third_party/WebKit/Source/modules/background_sync/SyncManager.cpp

Index: third_party/WebKit/Source/modules/background_sync/SyncManager.cpp
diff --git a/third_party/WebKit/Source/modules/background_sync/SyncManager.cpp b/third_party/WebKit/Source/modules/background_sync/SyncManager.cpp
index 459367201ca31b97e0398bf22db0b6e2233f7934..5f1ea85fc176221bc32320167018f84d4c877141 100644
--- a/third_party/WebKit/Source/modules/background_sync/SyncManager.cpp
+++ b/third_party/WebKit/Source/modules/background_sync/SyncManager.cpp
@@ -46,6 +46,14 @@ ScriptPromise SyncManager::registerFunction(ScriptState* scriptState, ExecutionC
     if (!m_registration->active())
         return ScriptPromise::rejectWithDOMException(scriptState, DOMException::create(AbortError, "Registration failed - no active Service Worker"));
 
+    if (scriptState->executionContext()->isDocument()) {
+        Document* document = toDocument(scriptState->executionContext());
+        if (!document->domWindow() || !document->frame())
+            return ScriptPromise::rejectWithDOMException(scriptState, DOMException::create(InvalidStateError, "Document is detached from window."));
+        if (!document->frame()->isMainFrame())
+            return ScriptPromise::rejectWithDOMException(scriptState, DOMException::create(AbortError, "Registration failed - not called from a main frame."));
+    }
+
     ScriptPromiseResolver* resolver = ScriptPromiseResolver::create(scriptState);
     ScriptPromise promise = resolver->promise();