Initial version of external_oes texture support and unit test

Committed: https://skia.googlesource.com/skia/+/27a048700778d4cebfc23301d1780649791b0e03

Review URL: https://codereview.chromium.org/1451683002
diff --git a/src/gpu/gl/GrGLInterface.cpp b/src/gpu/gl/GrGLInterface.cpp
index c6c846a..da3c656 100644
--- a/src/gpu/gl/GrGLInterface.cpp
+++ b/src/gpu/gl/GrGLInterface.cpp
@@ -727,8 +727,8 @@
     }
 
     if (fExtensions.has("EGL_KHR_image") || fExtensions.has("EGL_KHR_image_base")) {
-        if (nullptr == fFunctions.fCreateImage ||
-            nullptr == fFunctions.fDestroyImage) {
+        if (nullptr == fFunctions.fEGLCreateImage ||
+            nullptr == fFunctions.fEGLDestroyImage) {
             RETURN_FALSE_INTERFACE
         }
     }