Add --auto-open-devtools-for-tabs flag.

chrome/browser/devtools/devtools_auto_opener.h

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_DEVTOOLS_DEVTOOLS_AUTO_OPENER_H_
+#define CHROME_BROWSER_DEVTOOLS_DEVTOOLS_AUTO_OPENER_H_
+
+#include "chrome/browser/ui/browser_tab_strip_tracker.h"
+#include "chrome/browser/ui/tabs/tab_strip_model_observer.h"
+
+class DevToolsAutoOpener : public TabStripModelObserver {
+ public:
+  DevToolsAutoOpener();
+  ~DevToolsAutoOpener() override;
+
+ private:
+  // TabStripModelObserver overrides.
+  void TabInsertedAt(content::WebContents* contents,
+                     int index,
+                     bool foreground) override;
+
+  BrowserTabStripTracker browser_tab_strip_tracker_;
+
+  DISALLOW_COPY_AND_ASSIGN(DevToolsAutoOpener);
+};
+
+#endif  // CHROME_BROWSER_DEVTOOLS_DEVTOOLS_AUTO_OPENER_H_