Copy SpellChecker.{cpp,h} to SpellCheckRequester.{cpp.h}

Regarding ojan@'s suggestion(https://codereview.chromium.org/22732003/), this patch reverts r155831 which copies SpellChcker.{cpp,h} to SpellCheckerRequestManager.{cpp,h}, and copies SpellChecker.{cpp,h} to SpellCheckRequester.{cpp.h} for preparation of renaming SpellChecker class to SpellCheckRequester, to make class name more explicitly denotes what it does, and free its name to use name SpellChecker for decoupling spell checking and Editor class.

Note: Differences between original file and new file are for style checking in pre-submit.

BUG=n/a

Review URL: https://codereview.chromium.org/22475010

git-svn-id: svn://svn.chromium.org/blink/trunk@155920 bbb929c8-8fbe-4397-9dbb-9b2b20218538