For the groups:
- LogGroup.MOTION subfields now deteremined in Utils.writeMotionEvent() rather
  than in LatinKeyboardView.processMotionEvent()
- LogGroup.KEY is now logged throguh LatinIME.onCodeInput() rather than
  Utils.push().  This catches keys more generally, including modifiers, and
  records touch positions for everything.  Removed now-redundant
  Utils.writeBackspace() and Utils.writeChar().
- LogGroup.CORRECTION uses Utils.writeCorrection(), and formats instead of
  leaving this to callers.
- LogGroup.STATE_CHANGE uses Utils.writeStateChange().  Optional fields are
  still left to callers, as this group has more variety.

Formats have changed to incorporate new fields.

Minor housekeeping:

ENABLE_USABILITY_STUDY_LOG constants replaced with variable references, as
the logging feature can be changed in Settings and therefore dynamically
changes.

New log format:

20120322-111203.621+0900        1332382323621   s       [onStartInputView]      com.socialnmobile.dictapps.notepad.color.note   2131624043      147457  1140850694
20120322-111204.912+0900        1332382324912   m       [Down]  2782355 0       243     171     0.5666667       0.895
20120322-111204.975+0900        1332382324975   m       [Move]  2782419 0       240     171     0.6     1.17
20120322-111204.983+0900        1332382324983   m       [Move]  2782428 0       238     171     0.6     1.1899999
20120322-111204.992+0900        1332382324992   m       [Move]  2782437 0       236     171     0.6     1.1899999
20120322-111205.002+0900        1332382325002   m       [Move]  2782446 0       232     170     0.6     1.1899999
20120322-111205.012+0900        1332382325012   m       [Move]  2782456 0       227     169     0.6     1.125
20120322-111205.021+0900        1332382325021   m       [Move]  2782465 0       224     168     0.6     1.125
20120322-111205.031+0900        1332382325031   m       [Move]  2782475 0       221     167     0.6     0.895
20120322-111205.040+0900        1332382325040   m       [Move]  2782483 0       213     164     0.6     0.58
20120322-111205.047+0900        1332382325047   m       [Up]    2782491 0       213     164     0.6     0.58
20120322-111205.052+0900        1332382325052   k       'D'     243     171
20120322-111205.228+0900        1332382325228   m       [Down]  2782622 0       171     71      0.6333334       1.275
20120322-111205.243+0900        1332382325243   m       [Move]  2782677 0       178     69      0.6333334       1.275
20120322-111205.325+0900        1332382325325   m       [Up]    2782750 0       178     69      0.6333334       1.275
20120322-111205.333+0900        1332382325333   k       'e'     171     71
20120322-111205.509+0900        1332382325509   m       [Down]  2782936 0       265     139     0.53333336      0.885
20120322-111205.512+0900        1332382325512   m       [Move]  2782954 0       265     141     0.53333336      1.04
20120322-111205.552+0900        1332382325552   m       [Move]  2782973 0       265     143     0.5666667       1.14
20120322-111205.663+0900        1332382325663   m       [Up]    2783102 0       265     143     0.5666667       1.14
20120322-111205.668+0900        1332382325668   k       'f'     265     139
20120322-111206.140+0900        1332382326140   m       [Down]  2783584 0       348     352     0.53333336      0.675
20120322-111206.206+0900        1332382326206   m       [Move]  2783648 0       348     354     0.5666667       0.73499995
20120322-111206.223+0900        1332382326223   m       [Move]  2783666 0       348     356     0.5666667       0.545
20120322-111206.232+0900        1332382326232   m       [Up]    2783674 0       348     356     0.5666667       0.545
20120322-111206.236+0900        1332382326236   k       ' '     348     352
20120322-111206.245+0900        1332382326245   c       [----]  Def             -1

Bug: 6188932
Change-Id: Iea46a0c683f858b72005b8e81191ef1d70262dca