Add message and Help Center link to the chooser UI

chrome/browser/usb/usb_chooser_bubble_delegate.cc

Index: chrome/browser/usb/usb_chooser_bubble_delegate.cc
diff --git a/chrome/browser/usb/usb_chooser_bubble_delegate.cc b/chrome/browser/usb/usb_chooser_bubble_delegate.cc
index 61549c4f8dbe425a05dbc94acd064dd0a79d1260..5d89c567e480ea75b2cba0046cffc72b490a89cb 100644
--- a/chrome/browser/usb/usb_chooser_bubble_delegate.cc
+++ b/chrome/browser/usb/usb_chooser_bubble_delegate.cc
@@ -13,6 +13,7 @@
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/usb/usb_chooser_context.h"
 #include "chrome/browser/usb/usb_chooser_context_factory.h"
+#include "chrome/common/url_constants.h"
 #include "components/bubble/bubble_controller.h"
 #include "content/public/browser/render_frame_host.h"
 #include "content/public/browser/web_contents.h"
@@ -161,6 +162,10 @@ void UsbChooserBubbleDelegate::OnDeviceAdded(
   }
 }
 
+GURL UsbChooserBubbleDelegate::GetHelpCenterURL() const {
+  return GURL(chrome::kWebUsbHelpCenterURL);

[msw, 2016/02/17 01:31:35]

Does it make sense to link to a general support url for now?

[juncai, 2016/02/17 22:40:40]

A WebUsb help center URL has been requested, once the URL is available, I will
change it to that URL. I filed a bug to track it:
https://crbug.com/587525

+}
+
 void UsbChooserBubbleDelegate::OnDeviceRemoved(
     scoped_refptr<device::UsbDevice> device) {
   for (auto it = devices_.begin(); it != devices_.end(); ++it) {