This fixes a number of things that are warnings in the Mac compiler....

core/cross/display_mode.h

Index: core/cross/display_mode.h
===================================================================
--- core/cross/display_mode.h	(revision 21208)
+++ core/cross/display_mode.h	(working copy)
@@ -46,11 +46,11 @@
 class DisplayMode {
  public:
   DisplayMode()
-      : valid_(false),
-        width_(0),
+      : width_(0),
         height_(0),
         refresh_rate_(0),
-        id_(-1) {  // Since this is platform-specific, -1 may well be valid.
+        id_(-1),   // Since this is platform-specific, -1 may well be valid.
+        valid_(false) {
   }
   void Set(int w, int h, int r, int i) {
     width_ = w;