[headless] Expose DevToolsTarget via HeadlessBrowser + add tracing test.

headless/public/headless_browser.h

 // Copyright 2015 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 HEADLESS_PUBLIC_HEADLESS_BROWSER_H_
 #define HEADLESS_PUBLIC_HEADLESS_BROWSER_H_
 
 #include <memory>
 #include <string>
 #include <unordered_map>
@@ skipping 28 matching lines @@
 
   // Create a new browser context which can be used to create tabs and isolate
   // them from one another.
   // Pointer to HeadlessBrowserContext becomes invalid after:
   // a) Calling HeadlessBrowserContext::Close or
   // b) Calling HeadlessBrowser::Shutdown
   virtual HeadlessBrowserContext::Builder CreateBrowserContextBuilder() = 0;
 
   virtual std::vector<HeadlessBrowserContext*> GetAllBrowserContexts() = 0;
 
+  // Return a DevTools target corresponding to this tab. Note that this method

[Sami, 2017/04/26 15:47:06]

s/tab/browser/?

[Eric Seckler, 2017/04/27 09:14:20]

Uh, indeed! :)

+  // only returns a valid target after browser has been initialized on the main
+  // thread. The target only supports the domains available on the
+  // browser endpoint excluding the Tethering domain.
+  virtual HeadlessDevToolsTarget* GetDevToolsTarget() = 0;
+
   // Returns the HeadlessWebContents associated with the
   // |devtools_agent_host_id| if any.  Otherwise returns null.
   virtual HeadlessWebContents* GetWebContentsForDevToolsAgentHostId(
       const std::string& devtools_agent_host_id) = 0;
 
   // Returns HeadlessBrowserContext associated with the given id if any.
   // Otherwise returns null.
   virtual HeadlessBrowserContext* GetBrowserContextForId(
       const std::string& id) = 0;
 
@@ skipping 178 matching lines @@
 // the main loop, it will only return after HeadlessBrowser::Shutdown() is
 // called, returning the exit code for the process. It is not possible to
 // initialize the browser again after it has been torn down.
 int HeadlessBrowserMain(
     HeadlessBrowser::Options options,
     const base::Callback<void(HeadlessBrowser*)>& on_browser_start_callback);
 
 }  // namespace headless
 
 #endif  // HEADLESS_PUBLIC_HEADLESS_BROWSER_H_