[Android WebView] Add functionality to enable features and enable the spellcheck feature.
This patch adds the necessary generic methods to selectively enable a
feature in webview. The feature is only added if it is not yet enabled
(using --enable-features switch) and not disabled (using
--disable-features).
This patch also enables spellchecking in WebView by default, but only
on non low-end devices.
The feature can be disabled via the command line:
echo 'chrome --disable-features=AndroidSpellCheckerNonLowEnd' > \
/data/local/tmp/webview-command-line
BUG=583616, 629609
Review-Url: https://codereview.chromium.org/2396803002
Cr-Commit-Position: refs/heads/master@{#423513}
6 files changed
