Implement tab indicator for WebUSB.

chrome/browser/usb/web_usb_permission_provider.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/usb/web_usb_permission_provider.h"
 
 #include <stddef.h>
 #include <utility>
 
 #include "base/command_line.h"
 #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/browser/usb/usb_tab_helper.h"
 #include "chrome/common/chrome_switches.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/render_frame_host.h"
 #include "content/public/browser/web_contents.h"
 #include "device/usb/public/interfaces/device.mojom.h"
 
 using content::WebContents;
 using device::usb::WebUsbDescriptorSet;
 using device::usb::WebUsbConfigurationSubsetPtr;
 using device::usb::WebUsbFunctionSubsetPtr;
@@ skipping 82 matching lines @@
 bool WebUSBPermissionProvider::HasFunctionPermission(
     uint8_t requested_function,
     uint8_t configuration_value,
     const device::usb::DeviceInfo& device_info) const {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
   return FindOriginInDescriptorSet(
       device_info.webusb_allowed_origins.get(),
       render_frame_host_->GetLastCommittedURL().GetOrigin(),
       &configuration_value, &requested_function);
 }
+
+void WebUSBPermissionProvider::IncrementConnectionCount() {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+  WebContents* web_contents =
+      WebContents::FromRenderFrameHost(render_frame_host_);
+  UsbTabHelper* tab_helper = UsbTabHelper::FromWebContents(web_contents);

[miu, 2016/04/08 18:23:03]

Seems like this should be a call to GetOrCreateFromWebContents().  Unless you
know somehow that there *must* be a UsbTabHelper instance already associated
with the WebContents when the first increment occurs?  And, if that's the case,
consider whether you feel that's a safe assumption for the code here.

[Reilly Grant (use Gerrit), 2016/04/08 18:26:32]

Yes, if we've gotten here then there must be a UsbTabHelper as the UsbTabHelper
is what creates this object.

[miu, 2016/04/08 18:28:20]

Sounds good.  Just checking.  :)

+  tab_helper->IncrementConnectionCount();
+}
+
+void WebUSBPermissionProvider::DecrementConnectionCount() {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+  WebContents* web_contents =
+      WebContents::FromRenderFrameHost(render_frame_host_);
+  UsbTabHelper* tab_helper = UsbTabHelper::FromWebContents(web_contents);
+  tab_helper->DecrementConnectionCount();
+}