[Android] Simplify "network predictions" preference to a boolean value.

chrome/browser/net/prediction_options.h

Index: chrome/browser/net/prediction_options.h
diff --git a/chrome/browser/net/prediction_options.h b/chrome/browser/net/prediction_options.h
index 9029157db38d328c48f4ea0a269f8fceb86559f5..defc168e7852de70a0ea944614e97df845eb2e9e 100644
--- a/chrome/browser/net/prediction_options.h
+++ b/chrome/browser/net/prediction_options.h
@@ -18,6 +18,8 @@ namespace chrome_browser_net {
 // The numerical value is stored in the prefs file, therefore the same enum
 // with the same order must be used by the platform-dependent components.
 enum NetworkPredictionOptions {
+  // TODO(newt): collapse ALWAYS and WIFI_ONLY into a single value. Possibly

[newt (away), 2016/02/19 02:57:23]

mmenke: Should we keep this enum (and reduce it down to two values, or deprecate
the WIFI_ONLY value), or replace it with a boolean? The former option makes
migration easier (we could even avoid migration altogether). The latter option
seems simpler in the long run. Thoughts?

I'd like to do any changes here as a follow-up CL, though.

[mmenke, 2016/02/19 15:48:40]

My preference is to keep the enum, but get rid of the unused option (Which is
ALWAYS, not WIFI_ONLY, I believe?).

[newt (away), 2016/02/19 21:41:54]

Keeping the enum sounds good to me :)

Neither "ALWAYS" nor "WIFI_ONLY" is an accurate description of the "on" state
(which allows prerendering and prefetching on wi-fi only, but allows dns
preresolving and tcp preconnecting on all connection types). I think it makes
sense to rename the option that we keep to something like "ON" or "ENABLED" or
"ALLOWED".

+  // replace this enum with a boolean.
   NETWORK_PREDICTION_ALWAYS,
   NETWORK_PREDICTION_WIFI_ONLY,
   NETWORK_PREDICTION_NEVER,