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

chrome/browser/devtools/devtools_auto_opener.cc

+// 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.
+
+#include "chrome/browser/devtools/devtools_auto_opener.h"
+
+#include "base/command_line.h"
+#include "chrome/browser/devtools/devtools_window.h"
+
+DevToolsAutoOpener::DevToolsAutoOpener()
+    : browser_tab_strip_tracker_(this, nullptr, nullptr) {
+  browser_tab_strip_tracker_.Init(
+      BrowserTabStripTracker::InitWith::ALL_BROWERS);
+}
+
+DevToolsAutoOpener::~DevToolsAutoOpener() {
+}
+
+void DevToolsAutoOpener::TabInsertedAt(
+    content::WebContents* contents,
+    int index,
+    bool foreground) {
+  DevToolsWindow::OpenDevToolsWindow(contents);
+}