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 eb0cf4f30c8fb1a4bb321659c332e3e300f3173a..ad975824a363a61f19da48eaf392fcc0bbc0a116 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 {
@@ -1164,6 +1169,15 @@ void ChromeBrowserMainParts::PostBrowserStart() {
       base::TimeDelta::FromMinutes(1));
 #endif  // defined(ENABLE_WEBRTC)
 
+#if !defined(OS_ANDROID) && !defined(OS_IOS)
+  if (base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kEnableWebUsbNotifications)) {
+    webusb_browser_client_.reset(new ChromeWebUsbBrowserClient());
+    webusb::WebUsbBrowserClient::Set(webusb_browser_client_.get());
+    webusb_detector_.reset(new webusb::WebUsbDetector());

[stevenjb, 2015/08/28 16:55:05]

Couldn't this just be:
webusb_detector_.reset(new webusb::WebUsbDetector(webusb_browser_client_.get())?
Also:
We should destroy (reset) these explicitly in PostMainMessageLoopRun() so that
events do not occur after the message loop and the UI (e.g. the message center)
are destroyed.

[juncai, 2015/08/28 20:23:56]

Done.

+  }
+#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.