Part 1 of sample sprucing.

Part 1 of sample sprucing. Also, change chromium_extension.py to generate a random ID if the manifest doesn't have one.

* Create a test/data/extensions/samples directory and add
  Reader and Gmail samples to it.

* Minor fixes to buildbot sample to fit better visually.

* Minor fixes to bookmarks sample to use new button styles.

* Workaround for bug in bookmark sample where extension APIs do
  not load the first time.

* Move Resizer extension into samples/.

* Fix TabsAPI sample to not use old deprecated manifest
  properties anymore.

Part 2 will move the remaining samples into samples/ (don't want
to do that at the same time because git-cl doesn't know how to
tell Rietveld about moves and it would be confusing to review).

[Erik does not do reviews, 2009-04-29 15:24:30]

LGTM

one question:
Why check in the crx files?  We could add a build rule to generate them.  It
seems like this way, they'll always be out of date as people forget to update
them or the format changes.