Update the "Clear Browsing Data" dialogs to clear the EME/CDM data
when "Content Licenses" is selected. Currently selecting "Content
Licenses" only clears Flash data, if Flash is enabled.

Added new preference kDeleteMediaLicenses which replaces
kDeauthorizeContentLicenses, which was Flash specific. Default
value for kDeleteMediaLicenses is false, so the checkbox will
not be selected initially.

EME/CDM data is stored in the plugin private file system. If there
is no data saved for EME, then deletion is a nop. Actually deleting
the data was handled in https://codereview.chromium.org/1979733002/.

Changes to chrome://settings/clearBrowserData:
1) "Content licenses" is renamed to "Media Licenses".
2) "Content licenses" check box will always be displayed. (Currently
   it is only displayed if Flash is enabled.)
3) When selected, it will display an additional message as noted in
   the UI design doc (e.g. "You may lose access to premium content
   from some sites" or "You may lose access to premium content from
   www.youtube.com and some other sites.").

Changes to chrome://md-settings/advanced -> Clear Browsing Data
1) "Content licenses" is renamed to "Media Licenses".
2) When selected, it will display an additional message as noted
   above.

BUG=418195
TEST=tested "Clear Browsing Data" dialogs manually, new tests pass
CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2075023002
Cr-Commit-Position: refs/heads/master@{#403029}