Add support for OES_EGL_image_external and OES_EGL_image_external_essl3.

BUG=angleproject:1372

Change-Id: I8489e7fd0ab409b0775041ad5e9fbf0aab53886d
Reviewed-on: https://chromium-review.googlesource.com/344734
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Geoff Lang <geofflang@chromium.org>
diff --git a/src/libANGLE/validationES2.cpp b/src/libANGLE/validationES2.cpp
index 6e38100..309f223 100644
--- a/src/libANGLE/validationES2.cpp
+++ b/src/libANGLE/validationES2.cpp
@@ -1997,7 +1997,8 @@
             }
             break;
         case GL_TEXTURE_EXTERNAL_OES:
-            if (!context->getExtensions().eglStreamConsumerExternal)
+            if (!context->getExtensions().eglImageExternal &&
+                !context->getExtensions().eglStreamConsumerExternal)
             {
                 context->handleError(
                     Error(GL_INVALID_ENUM, "External texture extension not enabled"));