[blink] Add an InCustomSpellcheckDictionary marker

This patch adds InCustomSpellcheckDictionary marker. The marker is not a
part of MisspellingMarkers, because it does not mark a misspelling. It
marks a word that is in user's custom spellcheck dictionary. Chrome keeps
track of this word and its context to improve spellcheck quality.

The  marker will be used in upcoming patches. This patch is one of several
for issue 295190.

BUG=295190

Review URL: https://chromiumcodereview.appspot.com/24285008

git-svn-id: svn://svn.chromium.org/blink/trunk@158357 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Generate toCSSFooValue() for CSSCursorImageValue and CSSFontFaceSrcValue

This cl generates toCSSCursorImageValue() and toCSSFontFaceSrcValue() to cleanup static_cast<CSS*Value>.
toCSSFooValue() will help to detect bad-casts as well as improve readibility.

CSSFontFaceSrcValue uses DEFINE_CSS_VALUE_TYPE_CASTS instead of manual inline function.

BUG=N/A

Review URL: https://chromiumcodereview.appspot.com/24527002

git-svn-id: svn://svn.chromium.org/blink/trunk@158358 bbb929c8-8fbe-4397-9dbb-9b2b20218538