Reland of "Decrease the lag when switching between categories in the Cros wallpaper selector."

Reland of "Decrease the lag when switching between different categories in the Cros wallpaper selector".

The original one (https://codereview.chromium.org/1028513003) caused failures in the cros_trunk official builder (see http://master.chrome.corp.google.com:8011/builders/cros%20trunk/builds/31816 for detail).

The issue should fix the broken tests.

BUG=454932
Committed: https://crrev.com/392f1214c3e57ba1a69203072a8d97f10e39b330
Cr-Commit-Position: refs/heads/master@{#322602}

[xdai1, 2015-03-25 23:13:02]

xdai@chromium.org changed reviewers:
+ bshe@chromium.org

[xdai1, 2015-03-25 23:13:03]

Biao, please take another look at the CL, thanks! 
Basically I took your advice and only ran these two tests on official build
chrome, which should fix the failure of the tests.

[bshe, 2015-03-26 12:31:55]

On 2015/03/25 23:13:03, xdai1 wrote:
> Biao, please take another look at the CL, thanks! 
> Basically I took your advice and only ran these two tests on official build
> chrome, which should fix the failure of the tests.

huh, we lost coverage for chromium build this way. Although it is unlikely that
our
wallpaper app only works on official build but not on chromium build, it would
still be
safer/better to use the test to guard it. For chromium build, user expect to use
our app
to set a custom wallpaper. Would it possible to use enableOnlineWallpaper_ to
guard the test?

[xdai1, 2015-03-27 01:35:51]

On 2015/03/26 12:31:55, bshe wrote:
> On 2015/03/25 23:13:03, xdai1 wrote:
> > Biao, please take another look at the CL, thanks! 
> > Basically I took your advice and only ran these two tests on official build
> > chrome, which should fix the failure of the tests.
> 
> huh, we lost coverage for chromium build this way. Although it is unlikely
that
> our
> wallpaper app only works on official build but not on chromium build, it would
> still be
> safer/better to use the test to guard it. For chromium build, user expect to
use
> our app
> to set a custom wallpaper. Would it possible to use enableOnlineWallpaper_ to
> guard the test?

Biao, could you please take a look at Patch 6 and Patch 7? Basically they all
passed the tests, but if you click into the trybot results of Patch Set 7, you
will notice that the
BrowserGuestSessionNavigatorTest.Browser_Gets_Created_On_Visiting_Desktop failed
(with or without patch). The failure for this same test also can be observed in
Patch 3 and 4. Do you have a thought why it would happen? I think it might not
related with the change, but it's weird that Patch Set 2 and 6 don't have this
problem. Thanks for the help!

[bshe, 2015-03-27 17:22:12]

On 2015/03/27 01:35:51, xdai1 wrote:
> On 2015/03/26 12:31:55, bshe wrote:
> > On 2015/03/25 23:13:03, xdai1 wrote:
> > > Biao, please take another look at the CL, thanks! 
> > > Basically I took your advice and only ran these two tests on official
build
> > > chrome, which should fix the failure of the tests.
> > 
> > huh, we lost coverage for chromium build this way. Although it is unlikely
> that
> > our
> > wallpaper app only works on official build but not on chromium build, it
would
> > still be
> > safer/better to use the test to guard it. For chromium build, user expect to
> use
> > our app
> > to set a custom wallpaper. Would it possible to use enableOnlineWallpaper_
to
> > guard the test?
> 
> Biao, could you please take a look at Patch 6 and Patch 7? Basically they all
> passed the tests, but if you click into the trybot results of Patch Set 7, you
> will notice that the
> BrowserGuestSessionNavigatorTest.Browser_Gets_Created_On_Visiting_Desktop
failed
> (with or without patch). The failure for this same test also can be observed
in
> Patch 3 and 4. Do you have a thought why it would happen? I think it might not
> related with the change, but it's weird that Patch Set 2 and 6 don't have this
> problem. Thanks for the help!

From
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...
it looks like the test failed without your patch too. So it is not your problem.
It is probably because the test
is flaky. You can probably talk to chrome on ChromeOS gardener today.
the change lgtm

[xdai1, 2015-03-27 17:32:40]

On 2015/03/27 17:22:12, bshe wrote:
> On 2015/03/27 01:35:51, xdai1 wrote:
> > On 2015/03/26 12:31:55, bshe wrote:
> > > On 2015/03/25 23:13:03, xdai1 wrote:
> > > > Biao, please take another look at the CL, thanks! 
> > > > Basically I took your advice and only ran these two tests on official
> build
> > > > chrome, which should fix the failure of the tests.
> > > 
> > > huh, we lost coverage for chromium build this way. Although it is unlikely
> > that
> > > our
> > > wallpaper app only works on official build but not on chromium build, it
> would
> > > still be
> > > safer/better to use the test to guard it. For chromium build, user expect
to
> > use
> > > our app
> > > to set a custom wallpaper. Would it possible to use enableOnlineWallpaper_
> to
> > > guard the test?
> > 
> > Biao, could you please take a look at Patch 6 and Patch 7? Basically they
all
> > passed the tests, but if you click into the trybot results of Patch Set 7,
you
> > will notice that the
> > BrowserGuestSessionNavigatorTest.Browser_Gets_Created_On_Visiting_Desktop
> failed
> > (with or without patch). The failure for this same test also can be observed
> in
> > Patch 3 and 4. Do you have a thought why it would happen? I think it might
not
> > related with the change, but it's weird that Patch Set 2 and 6 don't have
this
> > problem. Thanks for the help!
> 
> From
>
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...
> it looks like the test failed without your patch too. So it is not your
problem.
> It is probably because the test
> is flaky. You can probably talk to chrome on ChromeOS gardener today.
> the change lgtm

Found the reason for the failure of the test:
https://code.google.com/p/chromium/issues/detail?id=469717. 
Thanks for the review!

[xdai1, 2015-03-27 17:34:39]

The CQ bit was checked by xdai@chromium.org

[commit-bot: I haz the power, 2015-03-27 17:35:00]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1038543002/120001

[commit-bot: I haz the power, 2015-03-27 17:55:27]

Committed patchset #7 (id:120001)

[commit-bot: I haz the power, 2015-03-27 17:56:15]

Patchset 7 (id:??) landed as
https://crrev.com/392f1214c3e57ba1a69203072a8d97f10e39b330
Cr-Commit-Position: refs/heads/master@{#322602}