Turn on UIPI for the GPU sandbox.

ui/gfx/gl/gl_switches.h

Index: ui/gfx/gl/gl_switches.h
===================================================================
--- ui/gfx/gl/gl_switches.h	(revision 93936)
+++ ui/gfx/gl/gl_switches.h	(working copy)
@@ -8,6 +8,16 @@
 #define UI_GFX_GL_GL_SWITCHES_H_
 #pragma once
 
+namespace gfx {
+
+// The GL implementation names that can be passed to --use-gl.
+extern const char kGLImplementationDesktopName[];
+extern const char kGLImplementationOSMesaName[];
+extern const char kGLImplementationEGLName[];
+extern const char kGLImplementationMockName[];
+
+}  // namespace gfx
+
 namespace switches {
 
 extern const char kDisableGpuVsync[];