[WebViewShell] retarget the shell to N for testing.

Increase targetSdkVersion to 24 to be able to execute
specific manual tests on N, e.g. geolocation api on
insecure origins.

BUG=603574

Review-Url: https://codereview.chromium.org/1942273003
Cr-Commit-Position: refs/heads/master@{#391485}
1 file changed