vk: Use proper externs for chrome.inputMethodPrivate.
vk: Use proper externs for chrome.inputMethodPrivate.

Currently, env is using chrome.input.ime.InputContext as the type of the
input context, but actually the real type is chrome.inputMethodPrivate.
InputContext. There are differences between the two (e.g. different fields).

Hence, we make the following changes:

1) Move InputContext externs to correct namespace.
   Reason: http://[]/javascript/externs/chrome_extensions.js?l=117&rcl=256056270

2) Add correct externs for chrome.inputMethodPrivate.

3) Change type of env to chrome.inputMethodPrivate.InputContext.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=266705217

ChadKillingsworth/closure-compiler,monetate/closure-compiler,monetate/closure-compiler,google/closure-compiler,vobruba-martin/closure-compiler,nawawi/closure-compiler,ChadKillingsworth/closure-compiler,nawawi/closure-compiler,ChadKillingsworth/closure-compiler,nawawi/closure-compiler,google/closure-compiler,monetate/closure-compiler,Yannic/closure-compiler,vobruba-martin/closure-compiler,google/closure-compiler,Yannic/closure-compiler,Yannic/closure-compiler,google/closure-compiler,ChadKillingsworth/closure-compiler,Yannic/closure-compiler,nawawi/closure-compiler,vobruba-martin/closure-compiler,vobruba-martin/closure-compiler,monetate/closure-compiler