Remove generated directories with 100s of files.

Remove generated directories with 100s of files.


BUG=
TEST=

Committed: https://code.google.com/p/dart/source/detail?r=5276

[Jacob, 2012-03-09 23:24:58]

Also updates the generator scripts to move dom_\w+\.dart  and html_\w+\.dart
generated files out of the root directory and into the generated subdirectory.
Fixed dom_dummy.dart to generate a single file so generated files do not need to
be checked in.

[vsm, 2012-03-10 00:02:28]

lgtm!

[sra1, 2012-03-10 04:59:03]

lgtm, except the subject should say "with thousands of files"