GitLab

Changes in this CL:
- Add cdm_factory.h to support platform specific CDM creation.
- Detach BrowserMediaPlayerManager from MediaDrmBridge.
- Store the security origin of CDMs in the manager so that CDMs don't need to
  know it.
- Keep the CDM ID in the manager so that CDMs don't see it.

BUG=338910
TEST=Test page plays and tests still pass.

Review URL: https://codereview.chromium.org/276973005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@271034 0039d316-1c4b-4281-b951-d872f2087c98