Add generator for packed GL enums.

For testing this also converts two unimportant GLenums, gl::BufferUsage
and gl::CullModeFace.

BUG=angleproject:2169

Change-Id: If1e86a97d0fed3fd567303aca6506ec579503076
Reviewed-on: https://chromium-review.googlesource.com/688000
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
diff --git a/src/tests/perf_tests/IndexDataManagerTest.cpp b/src/tests/perf_tests/IndexDataManagerTest.cpp
index bd105d7..99ed580 100644
--- a/src/tests/perf_tests/IndexDataManagerTest.cpp
+++ b/src/tests/perf_tests/IndexDataManagerTest.cpp
@@ -82,7 +82,7 @@
                       GLenum target,
                       const void *data,
                       size_t size,
-                      GLenum) override
+                      gl::BufferUsage) override
     {
         mData.resize(size);
         if (data && size > 0)
@@ -168,7 +168,7 @@
     }
     EXPECT_FALSE(mIndexBuffer
                      .bufferData(nullptr, GL_ARRAY_BUFFER, &indexData[0],
-                                 indexData.size() * sizeof(GLushort), GL_STATIC_DRAW)
+                                 indexData.size() * sizeof(GLushort), gl::BufferUsage::StaticDraw)
                      .isError());
 }