get genmipmap function in the struct

BUG=
R=bsalomon@google.com, reed@google.com

Author: humper@google.com

Review URL: https://chromiumcodereview.appspot.com/20436002

git-svn-id: http://skia.googlecode.com/svn/trunk@10393 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/gpu/gl/GrGLInterface.cpp b/src/gpu/gl/GrGLInterface.cpp
index f5cef11..72d7934 100644
--- a/src/gpu/gl/GrGLInterface.cpp
+++ b/src/gpu/gl/GrGLInterface.cpp
@@ -78,6 +78,9 @@
         NULL == fGenBuffers ||
         NULL == fGenTextures ||
         NULL == fGetBufferParameteriv ||
+#ifndef SKIA_IGNORE_GPU_MIPMAPS
+        NULL == fGenerateMipmap ||
+#endif
         NULL == fGetError ||
         NULL == fGetIntegerv ||
         NULL == fGetProgramInfoLog ||