DevTools: [CodeMirror] add listener for indentation setting
DevTools: [CodeMirror] add listener for indentation setting

This patch adds listener so that CodeMirrorTextEditor
will react on indentation setting change without
devtools reloading.

BUG=

Review URL: https://chromiumcodereview.appspot.com/18362003

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@153352 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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