Add webusb notification UI code

chrome/browser/chrome_browser_main.cc

Index: chrome/browser/chrome_browser_main.cc
diff --git a/chrome/browser/chrome_browser_main.cc b/chrome/browser/chrome_browser_main.cc
index 89733288609659f236749b4ac5df8f9f6604c5d3..ba15b751d37dcf61d65af13c47717a08b8c5ad13 100644
--- a/chrome/browser/chrome_browser_main.cc
+++ b/chrome/browser/chrome_browser_main.cc
@@ -235,6 +235,11 @@
 #include "ui/aura/env.h"
 #endif  // defined(USE_AURA)
 
+#if !defined(OS_ANDROID) && !defined(OS_IOS)
+#include "chrome/browser/chrome_webusb_browser_client.h"
+#include "components/webusb/webusb_detector.h"
+#endif
+
 using content::BrowserThread;
 
 namespace {
@@ -1140,6 +1145,15 @@ void ChromeBrowserMainParts::PostBrowserStart() {
       base::TimeDelta::FromMinutes(1));
 #endif  // defined(ENABLE_WEBRTC)
 
+#if !defined(OS_ANDROID) && !defined(OS_IOS)
+  scoped_ptr<webusb::WebUsbBrowserClient> webusb_browser_client_ptr(
+      new ChromeWebUsbBrowserClient());
+  if (webusb_browser_client_ptr->WebUsbNotificationEnabled()) {

[Reilly Grant (use Gerrit), 2015/08/21 17:23:02]

Why does this condition only guard the call to Set? Why create a
ChromeWebUsbBrowserClient and WebUsbDetector if the flag isn't enabled?

[juncai, 2015/08/21 20:18:27]

Done.

+    webusb::WebUsbBrowserClient::Set(webusb_browser_client_ptr.release());
+  }
+  webusb::WebUsbDetector::GetInstance();
+#endif
+
   // At this point, StartupBrowserCreator::Start has run creating initial
   // browser windows and tabs, but no progress has been made in loading
   // content as the main message loop hasn't started processing tasks yet.