Use CodeMirror for WebTry snippets.

CodeMirror (http://codemirror.net) is a rich code editor. This CL
adds the needed library and wires it with some minimal features, to
update the editor appearance to something like this:
http://codemirror.net/demo/theme.html?ambiance

We can later add Skia-customized features (custom keyword highlighting,
code completion, etc.).

(only tested locally)

R=jcgregorio@google.com, mtklein@google.com

Review URL: https://codereview.chromium.org/261693003

git-svn-id: http://skia.googlecode.com/svn/trunk@14499 2bbb7eff-a529-9590-31e7-b0007b416f81
14 files changed