First step in enabling creating tabs without an Activity on Android.

content/public/browser/content_browser_client.h

 // Copyright (c) 2012 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 CONTENT_PUBLIC_BROWSER_CONTENT_BROWSER_CLIENT_H_
 #define CONTENT_PUBLIC_BROWSER_CONTENT_BROWSER_CLIENT_H_
 
 #include <map>
 #include <string>
 #include <utility>
@@ skipping 598 matching lines @@
   virtual void OverridePageVisibilityState(
       RenderFrameHost* render_frame_host,
       blink::WebPageVisibilityState* visibility_state) {}
 
   // Allows an embedder to provide its own PresentationServiceDelegate
   // implementation. Returns nullptr if unavailable.
   virtual PresentationServiceDelegate* GetPresentationServiceDelegate(
       WebContents* web_contents);
 
   // Allows programmatic opening of a new tab/window without going through
-  // another WebContents. For example, from a Worker.
-  virtual WebContents* OpenURL(BrowserContext* browser_context,
-                               const OpenURLParams& params);
+  // another WebContents. For example, from a Worker. |callback| will be
+  // invoked with the appropriate WebContents* when available.
+  virtual void OpenURL(BrowserContext* browser_context,
+                       const OpenURLParams& params,
+                       const base::Callback<void(WebContents*)>& callback);
 
 #if defined(OS_POSIX) && !defined(OS_MACOSX)
   // Populates |mappings| with all files that need to be mapped before launching
   // a child process.
   virtual void GetAdditionalMappedFilesForChildProcess(
       const base::CommandLine& command_line,
       int child_process_id,
       FileDescriptorInfo* mappings) {}
 #endif
 
@@ skipping 12 matching lines @@
   // Allows an embedder to provide its own ExternalVideoSurfaceContainer
   // implementation.  Return nullptr to disable external surface video.
   virtual ExternalVideoSurfaceContainer*
   OverrideCreateExternalVideoSurfaceContainer(WebContents* web_contents);
 #endif
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_CONTENT_BROWSER_CLIENT_H_