Fix a DCHECK failure by registering a handler for 'dialogClose' message.

This fixes a DCHECK failure on chrome://print, where no handler was
registered to handle chrome.send("dialogClose").

BUG=416783

Review URL: https://codereview.chromium.org/614683002

Cr-Commit-Position: refs/heads/master@{#297199}

chrome/browser/ui/webui/constrained_web_dialog_ui.cc

@@ -60,6 +60,11 @@ ConstrainedWebDialogUI::~ConstrainedWebDialogUI() {
 
 void ConstrainedWebDialogUI::RenderViewCreated(
     RenderViewHost* render_view_host) {
+  // Add a "dialogClose" callback which matches WebDialogUI behavior.
+  web_ui()->RegisterMessageCallback("dialogClose",
+      base::Bind(&ConstrainedWebDialogUI::OnDialogCloseMessage,
+                 base::Unretained(this)));
+
   ConstrainedWebDialogDelegate* delegate = GetConstrainedDelegate();
   if (!delegate)
     return;
@@ -74,11 +79,6 @@ void ConstrainedWebDialogUI::RenderViewCreated(
     web_ui()->AddMessageHandler(*it);
   }
 
-  // Add a "dialogClose" callback which matches WebDialogUI behavior.
-  web_ui()->RegisterMessageCallback("dialogClose",
-      base::Bind(&ConstrainedWebDialogUI::OnDialogCloseMessage,
-                 base::Unretained(this)));
-
   dialog_delegate->OnDialogShown(web_ui(), render_view_host);
 }