Add verifiers for known certificate transparency logs

[kevinsawicki]

This pull request implements option 3 from #248 to fix the net::ERR_INSECURE_RESPONSE error that are happening in Electron 1.4.0 for certain requests.

/cc @deepak1556 @sleevi do you think this is right approach until Brightray can use URLRequestContextBuilder directly?

Closes #248
Refs electron/electron#7221
Upstream pull request electron/electron#7292

[sleevi]

C++ Style wise, I'd encourage a pattern more like

cert_transparency_verifier_.reset(new net::MultiLogCTVerifier());
cert_transparency_verifier_->AddLogs(net::ct::CreateLogVerifiersForKnownLogs());

This is preferred in general because should AddLogs throw an exception (which, admittedly, Chromium disables, but I'm speaking to the general C++ rule), then you'd end up with a memory leak, but if you assign to the unique_ptr<> first, then if AddLogs were to throw, you'd still end up with a graceful cleanup of memory.

But this is totally the Right Thing to do until you use a URLRequestContextBuilder, so looks good to me.

[kevinsawicki]

@sleevi thanks for the feedback, I've pushed up a new commit that incorporates it 👍

[deepak1556]

👍