[Quota] Disable requestQuota operation on non-Document context

This function should be unsupported on Workers, since it needs user interaction.

BUG=381528

Review URL: https://codereview.chromium.org/319053003

git-svn-id: svn://svn.chromium.org/blink/trunk@175639 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/modules/quota/StorageQuotaClient.cpp

@@ -43,6 +43,8 @@ const char* StorageQuotaClient::supplementName()
 
 StorageQuotaClient* StorageQuotaClient::from(ExecutionContext* context)
 {
+    if (!context->isDocument())
+        return 0;
     return static_cast<StorageQuotaClient*>(WillBeHeapSupplement<Page>::from(toDocument(context)->page(), supplementName()));
 }