Don't run macros or jsmin on extra snapshot scripts

Don't run macros or jsmin on extra snapshot scripts

js2c.py now distinguishes between the JS internal sources and any
extra scripts passed in. The latter only get validation and
comment/trailing whitespace removal applied now.

Also added a --js option to js2c.py, which will output a JS file
instead of a C++ file, for debugging. (I got tired of finding the
generated .cc file and extracting its byte array so that I could feed
it to a separate helper script I wrote.)

R=yangguo@chromium.org, jochen@chromium.org
BUG=v8:4064
LOG=N

Committed: https://crrev.com/8e2e83f0b37c0ef44c7b7f1892647d3d392e50d4
Cr-Commit-Position: refs/heads/master@{#28133}

[jochen (gone - plz use gerrit), 2015-04-29 12:09:06]

lgtm

[Yang, 2015-04-29 12:19:57]

On 2015/04/29 12:09:06, jochen wrote:
> lgtm

Lgtm

[domenic, 2015-04-29 13:36:57]

The CQ bit was checked by domenic@chromium.org

[commit-bot: I haz the power, 2015-04-29 13:37:02]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1117663002/1

[commit-bot: I haz the power, 2015-04-29 14:01:40]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-29 14:01:55]

Patchset 1 (id:??) landed as
https://crrev.com/8e2e83f0b37c0ef44c7b7f1892647d3d392e50d4
Cr-Commit-Position: refs/heads/master@{#28133}