New tabCapture.captureOffscreenTab API, initially for Presentation API 1UA mode

chrome/browser/extensions/api/tab_capture/offscreen_presentation.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 "chrome/browser/extensions/api/tab_capture/offscreen_presentation.h"
 
 #include <algorithm>
 
 #include "base/bind.h"
 #include "chrome/browser/extensions/api/tab_capture/tab_capture_registry.h"
@@ skipping 363 matching lines @@
   DCHECK_EQ(presentation_web_contents_.get(), contents);
 
   // This method is being called to check whether an extension is permitted to
   // capture the page.  Verify that the request is being made by the extension
   // that spawned this OffscreenPresentation.
 
   // Find the extension ID associated with the extension background page's
   // WebContents.
   content::BrowserContext* const extension_browser_context =
       owner_->extension_web_contents()->GetBrowserContext();
-  std::string extension_id;
-  for (const ExtensionHost* host :
-           ProcessManager::Get(extension_browser_context)->background_hosts()) {
-    if (host->host_contents() == owner_->extension_web_contents()) {
-      extension_id = host->extension_id();
-      break;
-    }
-  }
+  const extensions::Extension* const extension =
+      ProcessManager::Get(extension_browser_context)->
+          GetExtensionForWebContents(owner_->extension_web_contents());
+  const std::string extension_id = extension ? extension->id() : "";
+  LOG_IF(DFATAL, extension_id.empty())
+      << "Extension that started this OffscreenPresentation was not found.";
 
   // If verified, allow any tab capture audio/video devices that were requested.
   extensions::TabCaptureRegistry* const tab_capture_registry =
       extensions::TabCaptureRegistry::Get(extension_browser_context);
   content::MediaStreamDevices devices;
   if (tab_capture_registry && tab_capture_registry->VerifyRequest(
           request.render_process_id,
           request.render_frame_id,
           extension_id)) {
     if (request.audio_type == content::MEDIA_TAB_AUDIO_CAPTURE) {
@@ skipping 66 matching lines @@
 
   // Schedule the timer to check again in a second.
   capture_poll_timer_.Start(
       FROM_HERE,
       base::TimeDelta::FromSeconds(kPollIntervalInSeconds),
       base::Bind(&OffscreenPresentation::DieIfContentCaptureEnded,
                  base::Unretained(this)));
 }
 
 }  // namespace extensions