[Fetch API] Fix ScriptState leak in Fetch API unittests.

This CL fixes memory leaks caused by not calling disposePerContextData on
ScriptState.

BUG=524875

Review URL: https://codereview.chromium.org/1314333002

git-svn-id: svn://svn.chromium.org/blink/trunk@201299 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/modules/fetch/DataConsumerHandleTestUtil.cpp

@@ -44,6 +44,9 @@ void DataConsumerHandleTestUtil::Thread::initialize()
 void DataConsumerHandleTestUtil::Thread::shutdown()
 {
     m_executionContext = nullptr;
+    if (m_scriptState) {
+        m_scriptState->disposePerContextData();
+    }
     m_scriptState = nullptr;
     m_thread->shutdown();
     if (m_isolateHolder) {