Mac: make save/open dialogs operate as tab-modal sheets....

chrome/browser/login_prompt_mac.mm

Index: chrome/browser/login_prompt_mac.mm
diff --git a/chrome/browser/login_prompt_mac.mm b/chrome/browser/login_prompt_mac.mm
index 8a9e93c65c4c96f90cacb41d4877c236b066ba0d..c4384c2e1f7b319ce23e9a10123527b3f0fb780e 100644
--- a/chrome/browser/login_prompt_mac.mm
+++ b/chrome/browser/login_prompt_mac.mm
@@ -82,6 +82,17 @@ class LoginHandlerMac : public LoginHandler,
                                            std::wstring explanation) {
     DCHECK(MessageLoop::current() == ui_loop_);
 
+    TabContents* requesting_contents = GetTabContentsForLogin();
+    DCHECK(requesting_contents);
+
+    // If something goes wrong (e.g., there's already a tab-modal sheet up),
+    // cancel the authorization.
+    if (!requesting_contents ||
+        !requesting_contents->CanCreateConstrainedDialog()) {
+      CancelAuth();
+      return;
+    }
+
     // Load nib here instead of in constructor.
     sheet_controller_ = [[[LoginHandlerSheet alloc]
         initWithLoginHandler:this] autorelease];