Restrict usage of mesa headers to targets that really need them

ui/gl/gl_surface_osmesa.h

Index: ui/gl/gl_surface_osmesa.h
diff --git a/ui/gl/gl_surface_osmesa.h b/ui/gl/gl_surface_osmesa.h
index b4b48274913e2848c991b004c04fce808bde4c9d..472d7b115ed7828d158c020eeb0dbd7b2c3d0ef4 100644
--- a/ui/gl/gl_surface_osmesa.h
+++ b/ui/gl/gl_surface_osmesa.h
@@ -11,12 +11,14 @@
 
 namespace gfx {
 
+enum OSMesaSurfaceFormat { OSMesaSurfaceFormatBGRA, OSMesaSurfaceFormatRGBA };
+
 // A surface that the Mesa software renderer draws to. This is actually just a
 // buffer in system memory. GetHandle returns a pointer to the buffer. These
 // surfaces can be resized and resizing preserves the contents.
 class GL_EXPORT GLSurfaceOSMesa : public GLSurface {
  public:
-  GLSurfaceOSMesa(unsigned format, const gfx::Size& size);
+  GLSurfaceOSMesa(OSMesaSurfaceFormat format, const gfx::Size& size);
 
   // Implement GLSurface.
   virtual bool Initialize() OVERRIDE;