android: Allow registering multiple CreationParams

This is first step to avoid webapk overwriting default
CreationParams at run time. For now it's only used in
tests, and native side just hard codes the default ID.

Also added a check that warm up connection cannot be
used if the creation params do not match.

Other clean ups:
* Hide methods that don't need to be public.
* Remove copy. Params is already immutable.
* Remove redundant registerDefault call from
  Activities. Monochrome application already registers
  default in its onCreate.

BUG=664530

Review-Url: https://codereview.chromium.org/2705133002
Cr-Commit-Position: refs/heads/master@{#453428}