Initial KTX file decoder

R=bsalomon@google.com, robertphillips@google.com, halcanary@google.com, reed@google.com

Author: krajcevski@google.com

Review URL: https://codereview.chromium.org/302333002
diff --git a/gyp/gpu.gyp b/gyp/gpu.gyp
index fd81d60..f61a515 100644
--- a/gyp/gpu.gyp
+++ b/gyp/gpu.gyp
@@ -85,6 +85,7 @@
         'core.gyp:*',
         'utils.gyp:*',
         'etc1.gyp:libetc1',
+        'ktx.gyp:libSkKTX',
       ],
       'includes': [
         'gpu.gypi',