[Mac] Adds a flag to force 10.6-style fullscreen for testing.

chrome/browser/ui/cocoa/browser_window_cocoa.mm

Index: chrome/browser/ui/cocoa/browser_window_cocoa.mm
diff --git a/chrome/browser/ui/cocoa/browser_window_cocoa.mm b/chrome/browser/ui/cocoa/browser_window_cocoa.mm
index 64c15e4beb6995569266543275506cd9ecbc541f..290569affe379b4716c565123c2e5705d265996d 100644
--- a/chrome/browser/ui/cocoa/browser_window_cocoa.mm
+++ b/chrome/browser/ui/cocoa/browser_window_cocoa.mm
@@ -16,6 +16,7 @@
 #include "chrome/app/chrome_command_ids.h"
 #include "chrome/browser/download/download_shelf.h"
 #include "chrome/browser/extensions/tab_helper.h"
+#include "chrome/browser/fullscreen.h"
 #include "chrome/browser/password_manager/password_manager.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/shell_integration.h"
@@ -625,7 +626,7 @@ void BrowserWindowCocoa::OpenTabpose() {
 }
 
 void BrowserWindowCocoa::EnterFullscreenWithChrome() {
-  CHECK(base::mac::IsOSLionOrLater());
+  CHECK(chrome::mac::SupportsSystemFullscreen());
   if ([controller_ inPresentationMode])
     [controller_ exitPresentationMode];
   else
@@ -653,7 +654,7 @@ gfx::Rect BrowserWindowCocoa::GetInstantBounds() {
 WindowOpenDisposition BrowserWindowCocoa::GetDispositionForPopupBounds(
     const gfx::Rect& bounds) {
   // In Lion fullscreen mode, convert popups into tabs.
-  if (base::mac::IsOSLionOrLater() && IsFullscreen())
+  if (chrome::mac::SupportsSystemFullscreen() && IsFullscreen())
     return NEW_FOREGROUND_TAB;
   return NEW_POPUP;
 }