Add connection_options argument to ProofSource::GetProof

Add connection_options argument to ProofSource::GetProof

This CL adds a new argument to both overloads of ProofSource::GetProof,
permitting connection_options to be passed in.  Currently the
ProofSource ignores these arguments, but they will be employed shortly
for passing information about Mentat experiments.

Added connection_options arguments to ProofSource::GetProof, currently
unused.  No functional change intended, not flag-protected.

Merge internal change: 137083335

R=rch@chromium.org
BUG=

[danzh1, 2016-10-31 17:47:46]

The CQ bit was checked by danzh@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-10-31 17:48:05]

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

[Ryan Hamilton, 2016-10-31 18:28:00]

lgtm

[commit-bot: I haz the power, 2016-10-31 18:28:23]

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

[commit-bot: I haz the power, 2016-10-31 18:28:24]

Dry run: Try jobs failed on following builders:
  ios-simulator on master.tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/ios-simulator/bui...)