Convert TabHelper design doc to Markdown.

chrome/browser/ui/tab_helpers.h

 // Copyright 2014 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_UI_TAB_HELPERS_H_
 #define CHROME_BROWSER_UI_TAB_HELPERS_H_
 
 namespace content {
 class WebContents;
 }
 
 namespace chrome {
 class BrowserTabStripModelDelegate;
 
 namespace android {
 class ChromeWebContentsDelegateAndroid;
 }
 }
 
 namespace prerender {
 class PrerenderContents;
 }
 
 // A "tab contents" is a WebContents that is used as a tab in a browser window
 // (or the equivalent on Android). The TabHelpers class allows specific classes
 // to attach the set of tab helpers that is used for tab contents.
 //
-// https://www.chromium.org/developers/design-documents/tab-helpers
+// https://chromium.googlesource.com/chromium/src/+/master/docs/tab_helpers.md
 //
 // TODO(avi): This list is rather large, and for most callers it's due to the
 // fact that they need tab helpers attached early to deal with arbitrary
 // content loaded into a WebContents that will later be added to the tabstrip.
 // Is there a better way to handle this? (Ideally, this list would contain
 // only Browser and BrowserTabStripModelDelegate.)
 class TabHelpers {
  private:
   // Browser and its TabStripModelDelegate have intimate control of tabs.
   // TabAndroid is the equivalent on Android.
@@ skipping 18 matching lines @@
   // design document linked above, especially the section "Reusing tab helpers".
 
   // Adopts the specified WebContents as a full-fledged browser tab, attaching
   // all the associated tab helpers that are needed for the WebContents to
   // serve in that role. It is safe to call this on a WebContents that was
   // already adopted.
   static void AttachTabHelpers(content::WebContents* web_contents);
 };
 
 #endif  // CHROME_BROWSER_UI_TAB_HELPERS_H_