Add a comment about calling clearScriptObjects before clearForNavigation.

This is a follow up CL to r178818, adding a comment why the order is important.

BUG=364377
NOTRY=true

Review URL: https://codereview.chromium.org/460053002

git-svn-id: svn://svn.chromium.org/blink/trunk@180024 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/bindings/core/v8/ScriptController.cpp

@@ -421,6 +421,9 @@ void ScriptController::clearWindowShell()
     double start = currentTime();
     // V8 binding expects ScriptController::clearWindowShell only be called
     // when a frame is loading a new page. This creates a new context for the new page.
+
+    // The V8 context must be available for |clearScriptObjects()|.
+    // The below call must be before |clearForNavigation()| which disposes the V8 context.
     clearScriptObjects();
     m_windowShell->clearForNavigation();
     for (IsolatedWorldMap::iterator iter = m_isolatedWorlds.begin(); iter != m_isolatedWorlds.end(); ++iter)