[Android] Avoid unnecessary JNI calls for empty string conversions

[Android] Avoid unnecessary JNI calls for empty string conversions

There's no need to fetch/release the characters for an empty Java string
when converting it to native. Shortcut such cases by simply returning
an empty C++ string.

BUG=457748
NOTRY=true

Committed: https://crrev.com/e1f14701408e9174a4cd5251106ddd8a00d25f87
Cr-Commit-Position: refs/heads/master@{#341782}

[jdduke (slow), 2015-08-04 17:57:52]

jdduke@chromium.org changed reviewers:
+ nyquist@chromium.org

[jdduke (slow), 2015-08-04 17:57:52]

nyquist@: PTAL, thanks. I was thinking of ways we could consolidate logic
between UTF8/UTF16 here but it didn't quite seem worth it.

[nyquist, 2015-08-04 18:05:30]

https://codereview.chromium.org/1263333003/diff/20001/base/android/jni_string.cc
File base/android/jni_string.cc (right):

https://codereview.chromium.org/1263333003/diff/20001/base/android/jni_string...
base/android/jni_string.cc:35: return;
Do we need CheckException(env) here, since we're using the environment? (same
below)

[jdduke (slow), 2015-08-04 18:10:44]

https://codereview.chromium.org/1263333003/diff/20001/base/android/jni_string.cc
File base/android/jni_string.cc (right):

https://codereview.chromium.org/1263333003/diff/20001/base/android/jni_string...
base/android/jni_string.cc:35: return;
On 2015/08/04 18:05:29, nyquist wrote:
> Do we need CheckException(env) here, since we're using the environment? (same
> below)

Ohh good catch, done.

[nyquist, 2015-08-04 18:19:42]

The CQ bit was checked by nyquist@chromium.org

[nyquist, 2015-08-04 18:19:43]

lgtm

[commit-bot: I haz the power, 2015-08-04 18:19:51]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1263333003/40001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1263333003/40001

[commit-bot: I haz the power, 2015-08-04 18:48:56]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-08-04 18:48:56]

Try jobs failed on following builders:
  android_clang_dbg_recipe on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/android_clang_d...)
  cast_shell_android on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/cast_shell_andr...)

[jdduke (slow), 2015-08-04 19:06:49]

The CQ bit was checked by jdduke@chromium.org

[commit-bot: I haz the power, 2015-08-04 19:08:28]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1263333003/40001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1263333003/40001

[commit-bot: I haz the power, 2015-08-04 20:10:31]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-08-04 20:10:31]

Try jobs failed on following builders:
  win_chromium_rel_ng on tryserver.chromium.win (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_rel_...)

[jdduke (slow), 2015-08-04 20:25:28]

The CQ bit was checked by jdduke@chromium.org

[commit-bot: I haz the power, 2015-08-04 20:27:12]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1263333003/40001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1263333003/40001

[commit-bot: I haz the power, 2015-08-04 20:36:08]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-08-04 20:39:09]

Patchset 3 (id:??) landed as
https://crrev.com/e1f14701408e9174a4cd5251106ddd8a00d25f87
Cr-Commit-Position: refs/heads/master@{#341782}