Revert of speculative fix for ios (patchset #1 id:1 of https://codereview.chromium.org/637293003/)

Reason for revert:
Need to revert a90ed4e83897b45d6331ee4c54e1edd4054de9a8

Original issue's description:
> speculative fix for ios
>
> TBR=
>
> Committed: https://skia.googlesource.com/skia/+/96e89d5b45e8e293139ecd95302b5b4f07f8e9dc

TBR=
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/636153002
diff --git a/src/gpu/gl/iOS/SkCreatePlatformGLContext_iOS.mm b/src/gpu/gl/iOS/SkCreatePlatformGLContext_iOS.mm
index 2d56ef4..ce44dd3 100644
--- a/src/gpu/gl/iOS/SkCreatePlatformGLContext_iOS.mm
+++ b/src/gpu/gl/iOS/SkCreatePlatformGLContext_iOS.mm
@@ -13,7 +13,7 @@
 
 namespace {
 
-class IOSNativeGLContext : public SkGLContext {
+class IOSNativeGLContext : public SkNativeGLContext {
 public:
     IOSNativeGLContext();