Update skia's gyp to r1320.

Update skia's gyp to r1320.

Allows buildilng skia with make on OS X.

BUG=chromium:102033
Committed: https://code.google.com/p/skia/source/detail?r=3628

[thakis, 2012-04-09 04:56:49]

I also changed the svn:externals property on third_party/externals, but rietveld
doesn't show that for some reason.

[epoger, 2012-04-09 13:56:02]

LGTM

[epoger, 2012-04-09 14:03:17]

On 2012/04/09 13:56:02, epoger wrote:
> LGTM

Nico- thanks for adding this option.  Do you have any guidance on how developers
should choose whether to use makefile or xcode build?  Is one of them faster? 
Does it affect the developer's ability to use xcode IDE debugger?  etc.

[thakis, 2012-04-09 14:10:08]

On 2012/04/09 14:03:17, epoger wrote:
> On 2012/04/09 13:56:02, epoger wrote:
> > LGTM
> 
> Nico- thanks for adding this option.  Do you have any guidance on how
developers
> should choose whether to use makefile or xcode build?  Is one of them faster? 
> Does it affect the developer's ability to use xcode IDE debugger?  etc.

For chromium, the answer is: People who build from the commandline probably want
to use make. People who like using the xcode ide should continue using xcode.
For chrome, empty builds (i.e. nothing changed) were 6x faster with make
compared to xcodebuild. Since skia is a lot smaller, the difference is probably
smaller too but I'd expect it to be there.

(These days, the answer for chromium actually is the above with s/make/ninja/)

I don't know if one can use the xcode debugger when using the make build, I've
never tried.

These posts have a few numbers:
https://plus.google.com/101038813433650812235/posts/St5u7xTApoA
https://plus.google.com/101038813433650812235/posts/irc26fhRtPC

I'd say ask a few skia devs who work on a mac (I don't know how many there are)
to give it a try and then ask them what they think.