This interface allows an instance of the Runtime Memory Leak Detector
(components/metrics/leak_detector) to run on a non-browser process, such
as a tab (renderer) process. The interface provides two function APIs:

- GetParams(): Returns the profiling parameters used for initializing
  LeakDetector.
- SendLeakReports(): Passes an array of leak reports in serialized proto
  format (strings) to the browser process, where they can be attached to
  the UMA protobuf.

BUG=chromium:615223
TEST=Build successfully
R=asvitkine@chromium.org

Review-Url: https://codereview.chromium.org/2018983004
Cr-Commit-Position: refs/heads/master@{#396780}