Move TranslateStep enum into the Translate component core code.
This enum will be needed by the core Translate code. This CL moves it out of
TranslateTabHelper (which will stay in //chrome) into a standalone
translate_step.h file within the Translate component core code. It also renames
the enum values to be prefixed by TRANSLATE_STEP_ in accordance with naming
conventions for standalone enums (i.e., enums not defined within a class).
BUG=360002
TBR=jochen
Review URL: https://codereview.chromium.org/
227043002
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@262109 0039d316-1c4b-4281-b951-d872f2087c98