Add miniz library to third_party, use it on Windows

gyp/skflate.gyp

 # Target for including SkFlate.
 {
   'targets': [
     {
       'target_name': 'skflate',
       'type': 'static_library',
       'dependencies': [
         'skia_lib.gyp:skia_lib',
       ],
       'conditions': [
         # When zlib is not availible on a system,

[mtklein, 2014/08/13 17:57:09]

If this works out, might consider using miniz everywhere for our builds?  It's
API compatible with zlib, right?

[hal.canary, 2014/08/13 18:04:24]

Yes but Chromium and Android still use zlib everywhere.  Shouldn't we test that
when it is availible?

         # SkFlate::HaveFlate will just return false.
         [ 'skia_os != "win"',
           {
             'dependencies': [
               'zlib.gyp:zlib',
             ],
+          }, { # 'skia_os == "win"'
+            'dependencies': [
+              '../third_party/miniz/miniz.gyp:miniz'
+            ],
           }
         ],
       ],
       'sources': [
         '../src/core/SkFlate.cpp',
       ],
     },
   ],
 }