media: Refactor PlatformVerificationFlow.
Highlight of this CL:
- PlatformVerificationDialog and PlatformVerificationFlow are independant of
each other now.
- PlatformVerificationDialog is only triggered from
ProtectedMediaIdentifierPermissionContext::RequestPermission().
- ProxyDecryptor requests permission in certain conditions.
- PlatformVerificationFlow always checks permission before doing RA.
- ProtectedMediaIdentifierPermissionContext is the central place checking all
related settings and conditions, and handling the UI for ChromeOS.
This CL doesn't change the behavior on Android yet, which will be done in the
next CL.
BUG=455271,455262,446263
TBR=bauerb@chromium.org
TEST=Tested local test player and existing content providers's site/app.
Review URL: https://codereview.chromium.org/
1001723002
Cr-Commit-Position: refs/heads/master@{#320628}