headless: Require the user to pass in an initial URL

headless/lib/browser/headless_browser_impl.cc

 // 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.
 
 #include "headless/lib/browser/headless_browser_impl.h"
 
 #include "base/memory/ptr_util.h"
 #include "base/thread_task_runner_handle.h"
 #include "content/public/app/content_main.h"
 #include "content/public/browser/browser_thread.h"
@@ skipping 13 matching lines @@
     const HeadlessBrowser::Options& options)
     : on_start_callback_(on_start_callback),
       options_(options),
       browser_main_parts_(nullptr) {
   DCHECK(!on_start_callback_.is_null());
 }
 
 HeadlessBrowserImpl::~HeadlessBrowserImpl() {}
 
 std::unique_ptr<HeadlessWebContents> HeadlessBrowserImpl::CreateWebContents(
+    const GURL& initial_url,
     const gfx::Size& size) {
   DCHECK(BrowserMainThread()->BelongsToCurrentThread());
-  return base::WrapUnique(new HeadlessWebContentsImpl(
-      browser_context(), window_tree_host_->window(), size));
+  std::unique_ptr<HeadlessWebContentsImpl> web_contents =
+      base::WrapUnique(new HeadlessWebContentsImpl(
+          browser_context(), window_tree_host_->window(), size));
+  // We require the user to pass in an initial URL to ensure that the renderer
+  // gets initialized and eventually becomes ready to be inspected. See
+  // HeadlessWebContents::Observer::WebContentsReady.
+  if (!web_contents->OpenURL(initial_url))

[alex clarke (OOO till 29th), 2016/04/06 15:34:53]

Suppose this failed for some reason, how does the user find out why? (i.e. a 404
or maybe a dns lookup fail etc...)

[Sami, 2016/04/06 15:40:16]

The only reason this would fail immediately is if the URL is badly formed. 404s
and everything else will be communicated via the client API.

+    return nullptr;
+  return std::move(web_contents);
 }
 
 scoped_refptr<base::SingleThreadTaskRunner>
 HeadlessBrowserImpl::BrowserMainThread() const {
   return content::BrowserThread::GetMessageLoopProxyForThread(
       content::BrowserThread::UI);
 }
 
 void HeadlessBrowserImpl::Shutdown() {
   DCHECK(BrowserMainThread()->BelongsToCurrentThread());
@@ skipping 43 matching lines @@
   DCHECK(!options.message_pump);
 
   headless::HeadlessContentMainDelegate delegate(std::move(browser));
   content::ContentMainParams params(&delegate);
   params.argc = options.argc;
   params.argv = options.argv;
   return content::ContentMain(params);
 }
 
 }  // namespace headless