Enforce that only one constrained window is displayed at once per tab.

chrome/browser/tab_contents/tab_contents.h

Index: chrome/browser/tab_contents/tab_contents.h
diff --git a/chrome/browser/tab_contents/tab_contents.h b/chrome/browser/tab_contents/tab_contents.h
index ee25ef396e56789963b202d41ccd6e42da231bac..e0a104202a84fa46c4a06adcad6f95e9ae28e0be 100644
--- a/chrome/browser/tab_contents/tab_contents.h
+++ b/chrome/browser/tab_contents/tab_contents.h
@@ -7,6 +7,7 @@
 
 #include "build/build_config.h"
 
+#include <deque>
 #include <map>
 #include <set>
 #include <string>
@@ -343,9 +344,8 @@ class TabContents : public PageNavigator,
 
   // Create a new window constrained to this TabContents' clip and visibility.
   // The window is initialized by using the supplied delegate to obtain basic
-  // window characteristics, and the supplied view for the content. The window
-  // is sized according to the preferred size of the content_view, and centered
-  // within the contents.
+  // window characteristics, and the supplied view for the content. Note that
+  // the returned ConstrainedWindow might not yet be visible.
   ConstrainedWindow* CreateConstrainedDialog(
       ConstrainedWindowDelegate* delegate);
 
@@ -372,7 +372,7 @@ class TabContents : public PageNavigator,
   // Returns the number of constrained windows in this tab.  Used by tests.
   size_t constrained_window_count() { return child_windows_.size(); }
 
-  typedef std::vector<ConstrainedWindow*> ConstrainedWindowList;
+  typedef std::deque<ConstrainedWindow*> ConstrainedWindowList;
 
   // Return an iterator for the first constrained window in this tab contents.
   ConstrainedWindowList::iterator constrained_window_begin()