Fix relay session response parsing in PortAllocatorBase.
Fix relay session response parsing in PortAllocatorBase.

SplitStringIntoKeyValuePairs() wasn't used properly which was causing
response parsing to fail.

BUG=579733

Review URL: https://codereview.chromium.org/1617463002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#370581}

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk