port c7851da4 (r26419)

original commit message:

  Introduce LanguageMode, drop StrictMode.

  This enables adding more language modes in the future.

  For maximum flexibility, LanguageMode is a bitmask, so we're not restricted to
  use a sequence of language modes which are progressively stricter, but we can
  express the language mode as combination of features.

  For now, LanguageMode can only be "sloppy" or "strict", and there are
  STATIC_ASSERTS in places which need to change when more modes are added.

  LanguageMode is a bit like the old LanguageMode when "extended" mode was still
  around (see https://codereview.chromium.org/8417035 and
  https://codereview.chromium.org/181543002 ) except that it's transmitted through
  all the layers (there's no StrictModeFlag).

BUG=
R=weiliang.lin@intel.com

Review URL: https://codereview.chromium.org/902053005

Cr-Commit-Position: refs/heads/master@{#26514}