Restrict PPAPI Win32k lockdown to Win10 and above.
This patch restricts enabling Win32k lockdown for PPAPI processes to
Windows 10 and above. It includes a change to the flag text to indicate
it only works on Windows 10.

BUG=523278

Review-Url: https://codereview.chromium.org/2103153003
Cr-Commit-Position: refs/heads/master@{#402872}
2 files changed