[blink] Send InCustomSpellcheckDictionary markers to client

This patch includes the existing InCustomSpellcheckDictionary markers in
the list of markers that Blink sends to the client (the browser) along
with text to check. Before this patch, Blink sent only the existing
Spelling and Grammar markers. The browser keeps track of existing document
markers to improve the quality of spellcheck suggestions.

This patch is one of several for issue 295190 - "Add
InCustomSpellcheckDictionary marker to Blink for spellcheck feedback."

This patch depends on http://codereview.chromium.org/24582006.

BUG=295190

Review URL: https://chromiumcodereview.appspot.com/25137002

git-svn-id: svn://svn.chromium.org/blink/trunk@158497 bbb929c8-8fbe-4397-9dbb-9b2b20218538