Render conversations to 980px viewport

Expand all conversations to 980px width to allow double-tap to continue
to work on newer Chromium builds. See
https://codereview.chromium.org/18850005.

cool side effects
* much more usable double-tap zoom factor on KK+ (now "it just works")
* better text rendering fidelity in complex layouts (text no longer
  escapes bounds as it tended to do before)
* fixes text sizing edge cases where text was unexpectedly large and/or
  line heights messed with text rendering

Initially enable these changes on both JB- and KK+ WebViews. Disable
NARROW_COLUMNS layout on JB- to prevent very short columns.
pros on JB-: better rendering fidelity like on KK+, consistency with KK+
cons on JB-: some power users will miss pinch-then-double-tap-to-reflow
functionality

Possible future improvement: use device-width viewport when full convo
fits to inherit Chromium's new fast-click-handling behavior.

Bug: 12579959
Bug: 10695551
Change-Id: I13f85a6df909a966fcd0862e5bd292ec6ae77212
6 files changed