[DevTools] Check m_frontendPage in InspectorFrontendHost.

Source/core/inspector/InspectorFrontendHost.cpp

 /*
  * Copyright (C) 2007, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Matt Lilek <webkit@mattlilek.com>
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 128 matching lines @@
 void InspectorFrontendHost::disconnectClient()
 {
     m_client = 0;
     if (m_menuProvider)
         m_menuProvider->disconnect();
     m_frontendPage = nullptr;
 }
 
 void InspectorFrontendHost::setZoomFactor(float zoom)
 {
+    if (!m_frontendPage)

[pfeldman, 2014/09/06 10:30:29]

Why does this get called after disconnectClient?

[dgozman, 2014/09/06 10:36:27]

That's a reasonable question. The answer is: I don't know. I cannot repro the
crash, so I'm trying to fix it experimentally. If you have any idea, please
tell.

[pfeldman, 2014/09/06 10:42:29]

Could this be due to microtasks that are dispatching protocol messages?
disconnectClient is called from within willBeDestroyed, so theoretically things
could happen after it.

lgtm 

+        return;
     if (LocalFrame* frame = m_frontendPage->deprecatedLocalMainFrame())
         frame->setPageAndTextZoomFactors(zoom, 1);
 }
 
 float InspectorFrontendHost::zoomFactor()
 {
+    if (!m_frontendPage)
+        return 1;
     if (LocalFrame* frame = m_frontendPage->deprecatedLocalMainFrame())
         return frame->pageZoomFactor();
     return 1;
 }
 
 void InspectorFrontendHost::setInjectedScriptForOrigin(const String& origin, const String& script)
 {
+    if (!m_frontendPage)
+        return;
     m_frontendPage->inspectorController().setInjectedScriptForOrigin(origin, script);
 }
 
 void InspectorFrontendHost::copyText(const String& text)
 {
     Pasteboard::generalPasteboard()->writePlainText(text, Pasteboard::CannotSmartReplace);
 }
 
 static String escapeUnicodeNonCharacters(const String& str)
 {
@@ skipping 81 matching lines @@
 {
     return m_client && m_client->isUnderTest();
 }
 
 bool InspectorFrontendHost::isHostedMode()
 {
     return false;
 }
 
 } // namespace blink