Alternate approach to enabling PDF in gm (gyp changes)

Steve- Here is an alternate approach to http://codereview.appspot.com/4626071/ .

Highlights include:
- deletes skia_pdf_support flag: if your target depends on pdf.gyp, you get pdf support
- pdf.gyp now sets SK_PDF_SUPPORT and adds include/pdf dir for all targets that depend on it
- makes gypfiles smaller instead of bigger

Changes you made in http://codereview.appspot.com/4626071/ that are NOT included in this CL: (should we add them?)
- addition of zlib stuff
- change to SkPDFDevice::drawTextOnPath()

Tested as follows on both Mac and Linux, without any apparent problems:
make clean
make
out/Debug/tests
out/Debug/gm
[and ran SampleApp]

[Steve VanDeBogart, 2011-06-24 19:01:26]

LGTM

Should SampleApp.gyp also depend on PDF?

None of the generated PDFs will have compressed streams.  If you look in
src/core/SkFlate.cpp, if SK_ZLIB_INCLUDE isn't defined, compression isn't done. 
But currently, PDF is the only thing using zlib, so it only makes sense to
enable it (and link to it) when doing PDF.  I'll work on another CL to add a
SkFlate target and make pdf depend on that.

[epoger, 2011-06-24 19:10:08]

On 2011/06/24 19:01:26, Steve VanDeBogart wrote:
> LGTM
> 
> Should SampleApp.gyp also depend on PDF?

It already does...

> 
> None of the generated PDFs will have compressed streams.  If you look in
> src/core/SkFlate.cpp, if SK_ZLIB_INCLUDE isn't defined, compression isn't
done. 
> But currently, PDF is the only thing using zlib, so it only makes sense to
> enable it (and link to it) when doing PDF.  I'll work on another CL to add a
> SkFlate target and make pdf depend on that.

Sounds good.

Committed as r1713