Normalize JIDs when generating signatures for messages sent to CRD bot.

Normalize JIDs when generating signatures for messages sent to CRD bot.

When generating signatures for the messages sent to the bot the JID
must be normalized, i.e. node and domain parts must be in lower-case.
XmppSignalStrategy::GetLocalJid() was previously returning normalized
value, but it was changed recently, which broke hosts that use account
with upper-case characters in the name.

BUG=485134
Review URL: https://codereview.chromium.org/1131653002

Cr-Commit-Position: refs/heads/master@{#328646}
(cherry picked from commit 8916cd0a41e708d4c00e96dae7960cb9e634794e)

TBR=sergeyu@chromium.org

Committed: https://chromium.googlesource.com/chromium/src/+/1e71d8c0978c949e6589d459fba2428a5491558c

[Sergey Ulanov, 2015-05-07 22:58:11]

Committed patchset #1 (id:1) manually as
1e71d8c0978c949e6589d459fba2428a5491558c (presubmit successful).