Fetch WebView package even if it is uninstalled for the current user.

Since the WebView loading mechanism is global - it doesn't differ
between different users, a user for which the current WebView provider
is uninstalled won't be able to fetch any information about the current
provider without passing a certain flag (MATCH_UNINSTALLED_PACKAGES) to
the package manager.

Bug: 26677081
Change-Id: Id1b86164bb22fc7285d292da1b1115fb25e4d226