Allow server endpoint to be injected into the NetMetricsLogUploader from chrome/

As discussed in https://codereview.chromium.org/866163002/, this change will
allow consumer of the metrics component to configure the metrics uploader endpoint
without modifying the component.

BUG=453987

Review URL: https://codereview.chromium.org/886173002

Cr-Commit-Position: refs/heads/master@{#316915}
13 files changed