add SkGeometry.h to core.gypi

BUG=skia:
TBR=

Review URL: https://codereview.chromium.org/820683005
diff --git a/gyp/core.gypi b/gyp/core.gypi
index 63c9ca0..996b13d 100644
--- a/gyp/core.gypi
+++ b/gyp/core.gypi
@@ -98,6 +98,7 @@
         '<(skia_src_path)/core/SkFontStream.cpp',
         '<(skia_src_path)/core/SkFontStream.h',
         '<(skia_src_path)/core/SkGeometry.cpp',
+        '<(skia_src_path)/core/SkGeometry.h',
         '<(skia_src_path)/core/SkGlyphCache.cpp',
         '<(skia_src_path)/core/SkGlyphCache.h',
         '<(skia_src_path)/core/SkGlyphCache_Globals.h',