Initial work to get ETC1 data up to the GPU

gyp/gpu.gyp

 # GYP for building gpu
 {
   'target_defaults': {
     'conditions': [
       ['skia_os != "win"', {
         'sources/': [ ['exclude', '_win.(h|cpp)$'],
         ],
       }],
       ['skia_os != "mac"', {
         'sources/': [ ['exclude', '_mac.(h|cpp|m|mm)$'],
@@ skipping 66 matching lines @@
   },
   'targets': [
     {
       'target_name': 'skgpu',
       'product_name': 'skia_skgpu',
       'type': 'static_library',
       'standalone_static_library': 1,
       'dependencies': [
         'core.gyp:*',
         'utils.gyp:*',
+        'etc1.gyp:libetc1',
       ],
       'includes': [
         'gpu.gypi',
       ],
       'include_dirs': [
         '../include/gpu',
         '../src/core',
         '../src/gpu',
       ],
       'sources': [
@@ skipping 117 matching lines @@
             'libraries': [
               '-lGLESv2',
               '-lEGL',
             ],
           },
         }],
       ],
     },
   ],
 }