ash: Fix DesktopBackgroundController getting stuck.

ash: Fix DesktopBackgroundController getting stuck.

Fix an issue where DesktopBackgroundController gets confused
and stops switching wallpapers. The following sequence of
events triggers the bug:

a) Default wallpaper is requested and starts getting loaded
   from disk.
b) Before default wallpaper has been loaded, custom
   wallpaper is requested.
c) Default wallpaper is requested again.

At b), the default wallpaper load operation is canceled but
the WallpaperLoader object is retained. At c),
DesktopBackgroundController incorrectly sees the
still-present WallpaperLoader and believes that the default
wallpaper is still being loaded. This leaves
DesktopBackgroundController in a state where it never
switches back to the default wallpaper.

The fix is to disregard the existing WallpaperLoader if it
has already been canceled.

BUG=327443
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=242579

[Daniel Erat, 2013-12-26 20:52:00]

https://codereview.chromium.org/110463004/diff/1/ash/desktop_background/deskt...
File ash/desktop_background/desktop_background_controller.cc (left):

https://codereview.chromium.org/110463004/diff/1/ash/desktop_background/deskt...
ash/desktop_background/desktop_background_controller.cc:73: static void
LoadOnWorkerPoolThread(scoped_refptr<WallpaperLoader> loader) {
i don't know why this was a static method; making it be an instance method
instead

https://codereview.chromium.org/110463004/diff/1/ash/desktop_background/deskt...
File ash/desktop_background/desktop_background_controller.cc (right):

https://codereview.chromium.org/110463004/diff/1/ash/desktop_background/deskt...
ash/desktop_background/desktop_background_controller.cc:326:
!default_wallpaper_loader_->IsCanceled() &&
this is the fix

[DaveMoore, 2013-12-26 21:00:35]

lgtm

https://codereview.chromium.org/110463004/diff/1/ash/desktop_background/deskt...
File ash/desktop_background/desktop_background_controller.h (right):

https://codereview.chromium.org/110463004/diff/1/ash/desktop_background/deskt...
ash/desktop_background/desktop_background_controller.h:112: void
CancelDefaultWallpaperLoader();
Nit: Is the comment still correct?

[Daniel Erat, 2013-12-26 21:01:51]

https://codereview.chromium.org/110463004/diff/1/ash/desktop_background/deskt...
File ash/desktop_background/desktop_background_controller.h (right):

https://codereview.chromium.org/110463004/diff/1/ash/desktop_background/deskt...
ash/desktop_background/desktop_background_controller.h:112: void
CancelDefaultWallpaperLoader();
On 2013/12/26 21:00:35, DaveMoore wrote:
> Nit: Is the comment still correct?

Yes, but I'll update it to be a bit clearer. (Only "default" wallpaper gets
loaded by this class -- custom wallpaper is passed in as a gfx::ImageSkia.)

[commit-bot: I haz the power, 2013-12-26 21:04:26]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/derat@chromium.org/110463004/70001

[commit-bot: I haz the power, 2013-12-27 00:21:42]

Change committed as 242579