Initial version of external_oes texture support and unit test

src/gpu/gl/GrGLInterface.cpp

Index: src/gpu/gl/GrGLInterface.cpp
diff --git a/src/gpu/gl/GrGLInterface.cpp b/src/gpu/gl/GrGLInterface.cpp
index c6c846abf8ca59cee2d6f5a4f090d2271d2364d9..da3c656c18c36f16c51c96a7d72f962baafb20a2 100644
--- a/src/gpu/gl/GrGLInterface.cpp
+++ b/src/gpu/gl/GrGLInterface.cpp
@@ -727,8 +727,8 @@ bool GrGLInterface::validate() const {
     }
 
     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
         }
     }