Fix a crash when chooseDesktopMedia is called with no target tab

chrome/browser/extensions/api/desktop_capture/desktop_capture_api.cc

 // Copyright 2013 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/desktop_capture/desktop_capture_api.h"
 
+#include "ash/shell.h"
 #include "base/command_line.h"
 #include "base/compiler_specific.h"
 #include "base/strings/utf_string_conversions.h"
 #include "chrome/browser/extensions/extension_tab_util.h"
 #include "chrome/browser/media/desktop_media_list_ash.h"
 #include "chrome/browser/media/desktop_streams_registry.h"
 #include "chrome/browser/media/media_capture_devices_dispatcher.h"
 #include "chrome/browser/media/native_desktop_media_list.h"
 #include "chrome/browser/ui/ash/ash_util.h"
+#include "chrome/browser/ui/host_desktop.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/extensions/api/tabs.h"
 #include "content/public/browser/render_process_host.h"
 #include "content/public/browser/render_view_host.h"
 #include "content/public/browser/web_contents.h"
 #include "net/base/net_util.h"
 #include "third_party/webrtc/modules/desktop_capture/desktop_capture_options.h"
 #include "third_party/webrtc/modules/desktop_capture/screen_capturer.h"
 #include "third_party/webrtc/modules/desktop_capture/window_capturer.h"
 
@@ skipping 55 matching lines @@
   EXTENSION_FUNCTION_VALIDATE(args_->GetInteger(0, &request_id_));
   args_->Remove(0, NULL);
 
   scoped_ptr<api::desktop_capture::ChooseDesktopMedia::Params> params =
       api::desktop_capture::ChooseDesktopMedia::Params::Create(*args_);
   EXTENSION_FUNCTION_VALIDATE(params.get());
 
   DesktopCaptureRequestsRegistry::GetInstance()->AddRequest(
       render_view_host()->GetProcess()->GetID(), request_id_, this);
 
-  gfx::NativeWindow parent_window;
-  content::RenderViewHost* render_view;
+  gfx::NativeWindow parent_window = NULL;
+  content::RenderViewHost* render_view = NULL;
+  content::WebContents* web_contents = NULL;
   base::string16 target_name;
   if (params->target_tab) {
     if (!params->target_tab->url) {
       error_ = kNoUrlError;
       return false;
     }
     origin_ = GURL(*(params->target_tab->url)).GetOrigin();
 
     if (!CommandLine::ForCurrentProcess()->HasSwitch(
             switches::kAllowHttpScreenCapture) &&
         !origin_.SchemeIsSecure()) {
       error_ = kTabUrlNotSecure;
       return false;
     }
     target_name = base::UTF8ToUTF16(origin_.SchemeIsSecure() ?
         net::GetHostAndOptionalPort(origin_) : origin_.spec());
 
     if (!params->target_tab->id) {
       error_ = kNoTabIdError;
       return false;
     }
 
-    content::WebContents* web_contents = NULL;
     if (!ExtensionTabUtil::GetTabById(*(params->target_tab->id), GetProfile(),
                                       true, NULL, NULL, &web_contents, NULL)) {
       error_ = kInvalidTabIdError;
       return false;
     }
 
     GURL current_origin_ =
         web_contents->GetLastCommittedURL().GetOrigin();
     if (current_origin_ != origin_) {
       error_ = kTabUrlChangedError;
       return false;
     }
 
     // Register to be notified when the tab is closed.
     Observe(web_contents);
 
     render_view = web_contents->GetRenderViewHost();
     parent_window = web_contents->GetTopLevelNativeWindow();
   } else {
     origin_ = GetExtension()->url();
     target_name = base::UTF8ToUTF16(GetExtension()->name());
     render_view = render_view_host();
-    parent_window =
-        GetAssociatedWebContents()->GetTopLevelNativeWindow();
+
+    web_contents = GetAssociatedWebContents();
+    if (web_contents) {
+      parent_window = web_contents->GetTopLevelNativeWindow();
+    } else {
+#if defined(USE_ASH)
+      if (chrome::GetActiveDesktop() == chrome::HOST_DESKTOP_TYPE_ASH)
+        parent_window = ash::Shell::GetPrimaryRootWindow();

[sky, 2014/06/03 22:07:20]

Why is the primary root the right one here? And as this is async might you get
the wrong thing? Can't you get the information you need at creation time?

[tbarzic, 2014/06/03 22:25:33]

the primary root is used only when there is no web contents associated with the
extension function, e.g. when the function is called from background page, which
doesn't have a window associated with it (and no open browser windows, as
GetAssociatedWebContents will try to find the current browser's active web
contents in this case).
So this is essentially a fallback that's used when there's no other context to
use.
If you have a better option, I'm open to suggestions.

+#endif
+    }
   }
+
   render_process_id_ = render_view->GetProcess()->GetID();
   render_view_id_ = render_view->GetRoutingID();
 
   bool show_screens = false;
   bool show_windows = false;
 
   for (std::vector<api::desktop_capture::DesktopCaptureSourceType>::iterator
        it = params->sources.begin(); it != params->sources.end(); ++it) {
     switch (*it) {
       case api::desktop_capture::DESKTOP_CAPTURE_SOURCE_TYPE_NONE:
@@ skipping 50 matching lines @@
 #if defined(TOOLKIT_VIEWS) || defined(OS_MACOSX)
     picker_ = DesktopMediaPicker::Create();
 #else
     error_ = "Desktop Capture API is not yet implemented for this platform.";
     return false;
 #endif
   }
   DesktopMediaPicker::DoneCallback callback = base::Bind(
       &DesktopCaptureChooseDesktopMediaFunction::OnPickerDialogResults, this);
 
-  picker_->Show(web_contents(),
+  picker_->Show(web_contents,
                 parent_window, parent_window,
                 base::UTF8ToUTF16(GetExtension()->name()),
                 target_name,
                 media_list.Pass(), callback);
   return true;
 }
 
 void DesktopCaptureChooseDesktopMediaFunction::WebContentsDestroyed() {
   Cancel();
 }
@@ skipping 70 matching lines @@
 
 void DesktopCaptureRequestsRegistry::CancelRequest(int process_id,
                                                    int request_id) {
   RequestsMap::iterator it = requests_.find(RequestId(process_id, request_id));
   if (it != requests_.end())
     it->second->Cancel();
 }
 
 
 }  // namespace extensions