DevTools: provide the debugger detach reason in chrome.debugger.onDetach extension API.

chrome/browser/extensions/api/debugger/debugger_api.h

Index: chrome/browser/extensions/api/debugger/debugger_api.h
diff --git a/chrome/browser/extensions/api/debugger/debugger_api.h b/chrome/browser/extensions/api/debugger/debugger_api.h
index b7f332791f51d79ddadc2a31f9593d49399ece9f..603b02b5176175fd25264c267e0cffce0ca09096 100644
--- a/chrome/browser/extensions/api/debugger/debugger_api.h
+++ b/chrome/browser/extensions/api/debugger/debugger_api.h
@@ -21,6 +21,7 @@ class DictionaryValue;
 }
 
 namespace content {
+class DevToolsClientHost;
 class WebContents;
 }
 
@@ -80,4 +81,12 @@ class SendCommandDebuggerFunction : public DebuggerFunction {
   virtual bool RunImpl() OVERRIDE;
 };
 
+class DebuggerApi {
+ public:
+  // Marks ExtensionDevToolsClientHost as replaced with the bundled devtools
+  // so that we could report proper disconnect reason.
+  static void MarkDevToolsClientHostAsReplaced(
+      content::DevToolsClientHost* client_host);
+};
+
 #endif  // CHROME_BROWSER_EXTENSIONS_API_DEBUGGER_DEBUGGER_API_H_