Create the UserManager's Dialog Manager during init.

chrome/browser/ui/cocoa/profiles/user_manager_mac.mm

Index: chrome/browser/ui/cocoa/profiles/user_manager_mac.mm
diff --git a/chrome/browser/ui/cocoa/profiles/user_manager_mac.mm b/chrome/browser/ui/cocoa/profiles/user_manager_mac.mm
index 866b2192c788e88f7ec116760c18e0023cf03006..9cd790f7b9d6de890243873c086ffe9bec6ebad5 100644
--- a/chrome/browser/ui/cocoa/profiles/user_manager_mac.mm
+++ b/chrome/browser/ui/cocoa/profiles/user_manager_mac.mm
@@ -232,6 +232,12 @@ class ReauthDialogDelegate : public UserManager::ReauthDialogObserver,
   constrained_window_->CloseWebContentsModalDialog();
 }
 
+- (void)dealloc {
+  constrained_window_->CloseWebContentsModalDialog();
+
+  [super dealloc];
+}
+
 @end
 
 // Window controller for the User Manager view.
@@ -290,6 +296,13 @@ class ReauthDialogDelegate : public UserManager::ReauthDialogObserver,
     webContentsDelegate_.reset(new UserManagerWebContentsDelegate());
     webContents_->SetDelegate(webContentsDelegate_.get());
 
+    web_modal::WebContentsModalDialogManager::CreateForWebContents(
+        webContents_.get());
+    modal_manager_delegate_.reset(
+        new UserManagerModalManagerDelegate([[self window] contentView]));
+    web_modal::WebContentsModalDialogManager::FromWebContents(
+        webContents_.get())->SetDelegate(modal_manager_delegate_.get());
+
     [[NSNotificationCenter defaultCenter]
         addObserver:self
            selector:@selector(windowWillClose:)
@@ -351,14 +364,6 @@ class ReauthDialogDelegate : public UserManager::ReauthDialogObserver,
 }
 
 - (void)showReauthDialogWithProfile:(Profile*)profile email:(std::string)email {
-  // Make sure there's a WebContentsModalDialogManager for this UserManager's
-  // web contents.
-  web_modal::WebContentsModalDialogManager::CreateForWebContents(
-      webContents_.get());
-  modal_manager_delegate_.reset(
-      new UserManagerModalManagerDelegate([[self window] contentView]));
-  web_modal::WebContentsModalDialogManager::FromWebContents(
-      webContents_.get())->SetDelegate(modal_manager_delegate_.get());
   reauth_window_controller_.reset(
       [[ReauthDialogWindowController alloc]
           initWithProfile:profile