DevTools: Add an ASSERT to explore possible reasons of test failures.

BUG=408910

Review URL: https://codereview.chromium.org/544553002

git-svn-id: svn://svn.chromium.org/blink/trunk@181670 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/inspector/InspectorWorkerAgent.cpp

@@ -59,6 +59,7 @@ public:
         , m_id(s_nextId++)
         , m_connected(false)
     {
+        ASSERT(!proxy->pageInspector());
     }
     virtual ~WorkerFrontendChannel()
     {