DevTools: respond with error when Debugger command is sent to disabled debugger agent

Source/core/inspector/InspectorDOMDebuggerAgent.cpp

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 119 matching lines @@
 {
     if (m_domAgent->enabled() && m_debuggerAgent->enabled())
         m_instrumentingAgents->setInspectorDOMDebuggerAgent(this);
 }
 
 void InspectorDOMDebuggerAgent::domAgentWasDisabled()
 {
     disable(nullptr);
 }
 
+bool InspectorDOMDebuggerAgent::checkEnabled(ErrorString* errorString)
+{
+    if (!m_domAgent->enabled()) {
+        *errorString = "DOM domain required by DOMDebugger is not enabled";
+        return false;
+    }
+    if (!m_debuggerAgent->enabled()) {
+        *errorString = "Debugger domain required by DOMDebugger is not enabled";
+        return false;
+    }
+    return true;
+}
+
 void InspectorDOMDebuggerAgent::disable(ErrorString*)
 {
     m_instrumentingAgents->setInspectorDOMDebuggerAgent(nullptr);
     clear();
 }
 
 void InspectorDOMDebuggerAgent::discardAgent()
 {
     m_debuggerAgent->setListener(nullptr);
     m_debuggerAgent = nullptr;
@@ skipping 440 matching lines @@
     eventData->setString("url", url);
     m_debuggerAgent->breakProgram(InspectorFrontend::Debugger::Reason::XHR, eventData.release());
 }
 
 void InspectorDOMDebuggerAgent::clear()
 {
     m_domBreakpoints.clear();
 }
 
 } // namespace blink