Add perf test for ushort DrawElements.

The code path in the D3D11 back-end is sigificantly different for
unsigned short indices vs unsigned int. Because of the workaround we
have for the primitive restart index in D3D11, ushort rendering can
be slower.

BUG=angleproject:2229

Change-Id: I303dcc55b0314ec45508044995ba47b250cbb87d
Reviewed-on: https://chromium-review.googlesource.com/767149
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
diff --git a/src/common/utilities.cpp b/src/common/utilities.cpp
index 80abdd9..ebe8a7a 100644
--- a/src/common/utilities.cpp
+++ b/src/common/utilities.cpp
@@ -833,6 +833,22 @@
     }
 }
 
+unsigned int ElementTypeSize(GLenum elementType)
+{
+    switch (elementType)
+    {
+        case GL_UNSIGNED_BYTE:
+            return sizeof(GLubyte);
+        case GL_UNSIGNED_SHORT:
+            return sizeof(GLushort);
+        case GL_UNSIGNED_INT:
+            return sizeof(GLuint);
+        default:
+            UNREACHABLE();
+            return 0;
+    }
+}
+
 }  // namespace gl
 
 namespace egl