Unbreak gn build of net_unittests on Android

Unbreak gn build of net_unittests on Android

/net/test/run_all_unittests.cc references url::android::RegisterJni
which is defined in url/android/url_jni_registrar.h. url/BUILD.gn only
includes the latter when building
url_lib_use_icu_alternatives_on_android, but not when building url_lib.

Conditionalize the use of url::android::RegisterJni so that it's only
invoked when USE_ICU_ALTERNATIVE_ON_ANDROID is defined. I.e. Only use
url::android::RegisterJni when the current build target is depending on
url_lib_use_icu_alternatives_on_android.

BUG=none

Committed: https://crrev.com/ca61186fc5e11cc2acb59c3d2f28016f246ce807
Cr-Commit-Position: refs/heads/master@{#351387}

[asanka, 2015-09-28 21:06:24]

asanka@chromium.org changed reviewers:
+ abarth@chromium.org

[asanka, 2015-09-28 21:37:51]

asanka@chromium.org changed reviewers:
- abarth@chromium.org

[asanka, 2015-09-29 18:05:18]

asanka@chromium.org changed reviewers:
+ xunjieli@chromium.org

[asanka, 2015-09-29 18:16:31]

PTAL?

[xunjieli, 2015-09-29 18:20:46]

On 2015/09/29 18:16:31, asanka wrote:
> PTAL?

The change makes sense. LGTM. Thanks!

[asanka, 2015-09-29 20:19:33]

On 2015/09/29 at 18:20:46, xunjieli wrote:
> On 2015/09/29 18:16:31, asanka wrote:
> > PTAL?
> 
> The change makes sense. LGTM. Thanks!

Thanks!

[asanka, 2015-09-29 20:19:37]

The CQ bit was checked by asanka@chromium.org

[commit-bot: I haz the power, 2015-09-29 20:20:21]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1373103002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1373103002/20001

[commit-bot: I haz the power, 2015-09-29 20:26:45]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-09-29 20:27:41]

Patchset 2 (id:??) landed as
https://crrev.com/ca61186fc5e11cc2acb59c3d2f28016f246ce807
Cr-Commit-Position: refs/heads/master@{#351387}