[Media Capabilities] Rename query() to decodingInfo() and MediaDecodingAbility to MediaCapabilitiesInfo

This is matching recent spec changes:
https://github.com/WICG/media-capabilities/pull/31

The MediaConfiguration changes are not reflected in this CL.

BUG=690380
R=mcasas@chromium.org,sandersd@chromium.org

Review-Url: https://codereview.chromium.org/2807713002
Cr-Commit-Position: refs/heads/master@{#463403}
19 files changed