Allow null jstring to C++ string conversions in release.

Allow null jstring to C++ string conversions in release.

WebView has too many cases where apps can pass in a null java string and
have it reach native causing a crash. For now, put back the code that
returned empty string, but keep the DCHECK so that we still hit it on
bots that run with DCHECKs enabled. We'll fix WebView and have another
go at this in a later release.

This is a partial revert of https://codereview.chromium.org/1828193002

BUG=597564
Review URL: https://codereview.chromium.org/1913183002

Cr-Commit-Position: refs/heads/master@{#389166}
(cherry picked from commit 075418c032dd093e52aef9e56b8a3eb55eb7dc58)

Committed: https://chromium.googlesource.com/chromium/src/+/35f63706d80bd84b2f5ccd5e5f251243a7805731

[Torne, 2016-04-25 10:12:56]

Description was changed from

==========
Allow null jstring to C++ string conversions in release.

WebView has too many cases where apps can pass in a null java string and
have it reach native causing a crash. For now, put back the code that
returned empty string, but keep the DCHECK so that we still hit it on
bots that run with DCHECKs enabled. We'll fix WebView and have another
go at this in a later release.

This is a partial revert of https://codereview.chromium.org/1828193002

BUG=597564

Review URL: https://codereview.chromium.org/1913183002

Cr-Commit-Position: refs/heads/master@{#389166}
(cherry picked from commit 075418c032dd093e52aef9e56b8a3eb55eb7dc58)
==========

to

==========
Allow null jstring to C++ string conversions in release.

WebView has too many cases where apps can pass in a null java string and
have it reach native causing a crash. For now, put back the code that
returned empty string, but keep the DCHECK so that we still hit it on
bots that run with DCHECKs enabled. We'll fix WebView and have another
go at this in a later release.

This is a partial revert of https://codereview.chromium.org/1828193002

BUG=597564

Review URL: https://codereview.chromium.org/1913183002

Cr-Commit-Position: refs/heads/master@{#389166}
(cherry picked from commit 075418c032dd093e52aef9e56b8a3eb55eb7dc58)

Committed:
https://chromium.googlesource.com/chromium/src/+/35f63706d80bd84b2f5ccd5e5f25...
==========

[Torne, 2016-04-25 10:12:57]

Committed patchset #1 (id:1) manually as
35f63706d80bd84b2f5ccd5e5f251243a7805731.