Expose ConvertLangCodeForTranslation and use it when converting the UX language
for all platforms (the performance hit should be negligible and this way
it is more legible than adding a #ifdef Android)
Fix a few unrelated typos on comments while at it.
BUG=311624
Review URL: https://codereview.chromium.org/68823004
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234706 0039d316-1c4b-4281-b951-d872f2087c98