DevTools: [DefaultTextEditor] kill DefaultTextEditor

This patch:
- Removes DefaultTextEditor code from the source-code
- Removes unused classes from textEditor.css
- Additionally adds a 'position:relative' rule for CodeMirrorTextEditor
element. This makes it possible to set up a fixed height in
editor-test.js

BUG=

Review URL: https://chromiumcodereview.appspot.com/19723007

git-svn-id: svn://svn.chromium.org/blink/trunk@154577 bbb929c8-8fbe-4397-9dbb-9b2b20218538