Small improvements to JNI references.

Small improvements to JNI references.

Add a move constructor and move assignment operator to local, global and
weak references to reduce reference churn (saves a small number of bytes).
Allow weak references to be constructed from JavaRef.
Replace NULL with nullptr in jni_weak_ref code.

BUG=

Committed: https://crrev.com/c6bc15dbab488636bb2f2ddff615ffacfc50c5a8
Cr-Commit-Position: refs/heads/master@{#414444}

[Torne, 2016-08-22 12:44:04]

torne@chromium.org changed reviewers:
+ rmcilroy@chromium.org

[rmcilroy, 2016-08-22 15:14:08]

lgtm

[Torne, 2016-08-22 15:18:41]

The CQ bit was checked by torne@chromium.org

[commit-bot: I haz the power, 2016-08-22 15:19:09]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-08-22 16:14:38]

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

[commit-bot: I haz the power, 2016-08-22 16:14:39]

Try jobs failed on following builders:
  android_clang_dbg_recipe on master.tryserver.chromium.android (JOB_FAILED,
https://build.chromium.org/p/tryserver.chromium.android/builders/android_clan...)

[Torne, 2016-08-25 14:36:45]

The CQ bit was checked by torne@chromium.org

[Torne, 2016-08-25 14:36:45]

The patchset sent to the CQ was uploaded after l-g-t-m from
rmcilroy@chromium.org
Link to the patchset: https://codereview.chromium.org/2268553002/#ps20001
(title: "Learn about, and then fix, the most vexing parse. :)")

[commit-bot: I haz the power, 2016-08-25 14:37:26]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-08-25 15:43:15]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2016-08-25 15:44:23]

Description was changed from

==========
Small improvements to JNI references.

Add a move constructor and move assignment operator to local, global and
weak references to reduce reference churn (saves a small number of bytes).
Allow weak references to be constructed from JavaRef.
Replace NULL with nullptr in jni_weak_ref code.

BUG=
==========

to

==========
Small improvements to JNI references.

Add a move constructor and move assignment operator to local, global and
weak references to reduce reference churn (saves a small number of bytes).
Allow weak references to be constructed from JavaRef.
Replace NULL with nullptr in jni_weak_ref code.

BUG=

Committed: https://crrev.com/c6bc15dbab488636bb2f2ddff615ffacfc50c5a8
Cr-Commit-Position: refs/heads/master@{#414444}
==========

[commit-bot: I haz the power, 2016-08-25 15:44:24]

Patchset 2 (id:??) landed as
https://crrev.com/c6bc15dbab488636bb2f2ddff615ffacfc50c5a8
Cr-Commit-Position: refs/heads/master@{#414444}