Update libchromiumcontent to get its Python scripts

* vendor/libchromiumcontent 3f6f01c...588f368 (17):
  > Merge pull request #8 from aroben/menu-controller
  > Merge pull request #6 from aroben/shell_dialogs
  > Fix typo in script/create-dist
  > Merge pull request #5 from aroben/python
  > Add libtest_support_chromiumcontent.a
  > Build and distribute libgtest.a
  > Stop trying to compile SQLitePersistentCookieStore separately
  > Update to latest Chromium trunk revision
  > Merge pull request #4 from aroben/atom
  > Actually compile the base/prefs code
  > Export symbols from base/prefs
  > Compile and export SQLitePersistentCookieStore
  > Export webkit/plugins headers
  > Export skia/ext headers
  > Export ui/surface headers, too
  > Export Skia symbols from libchromiumcontent
  > Update to match chrome/trunk
Rewrite script/boostrap in Python

This is the first step toward supporting Windows.
Rewrite script/build in Python

The script is still Mac-specific, but this will make it easier to add
Windows support later.
Merge pull request #12 from aroben/python

Rewrite scripts in Python