Make all gyp targets automatically include common.gypi

Make all gyp targets automatically include common.gypi

Do this, rather than including common.gypi explicitly in all our gyp files, so that gyp files we use but do not maintain (e.g., third_party/externals/libjpeg/libjpeg.gyp) will include common.gypi too.
Committed: https://code.google.com/p/skia/source/detail?r=3411

[epoger, 2012-03-15 20:41:37]

If/when I land this change I will ping seanpaul to make sure I'm not breaking
his world with this change. See his http://codereview.appspot.com/5023042
('Refactor the bench and common gyp/gypi files to allow for building bench
within')

[bsalomon, 2012-03-16 13:17:04]

On 2012/03/15 20:41:37, epoger wrote:
> If/when I land this change I will ping seanpaul to make sure I'm not breaking
> his world with this change. See his http://codereview.appspot.com/5023042
> ('Refactor the bench and common gyp/gypi files to allow for building bench
> within')

LGTM