Fix devtools bugs Fix a spurious layout test failure

Source/core/inspector/InspectorDebuggerAgent.h

Index: Source/core/inspector/InspectorDebuggerAgent.h
diff --git a/Source/core/inspector/InspectorDebuggerAgent.h b/Source/core/inspector/InspectorDebuggerAgent.h
index d017213a4ac04098be67242eafb02282add6829e..929aeab4aa8a3997c61a7fccb0c42db112b964c7 100644
--- a/Source/core/inspector/InspectorDebuggerAgent.h
+++ b/Source/core/inspector/InspectorDebuggerAgent.h
@@ -200,7 +200,7 @@ public:
     // it returns a value, don't call the v8Agent. The v8Agent has no idea the
     // dartAgent exists but the dartAgent was built with the knowledge that
     // there could be other agents around.
-    DartInspectorDebuggerAgent* dartAgent() { return 0; }
+    virtual DartInspectorDebuggerAgent* dartAgent() { return 0; }
 
 protected:
     InspectorDebuggerAgent(InjectedScriptManager*, v8::Isolate*);