Enable font size inflation for Android native mobile browser. (Bug 627842, patch 18)

This applies the same patch made to the default preferences of XUL
fennec (mobile/xul/app/mobile.js) in Bug 627842, patch 4 (changeset
d3e230bec2f9, r=roc) to the default preferences of Android Fennec.

mobile/android/app/mobile.js

@@ -420,6 +420,8 @@ pref("browser.ui.zoom.animationDuration", 200); // ms duration of double-tap zoo
 pref("browser.ui.zoom.reflow", false); // Change text wrapping on double-tap
 pref("browser.ui.zoom.reflow.fontSize", 720);
 
+pref("font.size.inflation.minTwips", 160);
+
 // pinch gesture
 pref("browser.ui.pinch.maxGrowth", 150);     // max pinch distance growth
 pref("browser.ui.pinch.maxShrink", 200);     // max pinch distance shrinkage