Implement tab indicator for WebUSB.

chrome/browser/usb/web_usb_permission_provider.cc

Index: chrome/browser/usb/web_usb_permission_provider.cc
diff --git a/chrome/browser/usb/web_usb_permission_provider.cc b/chrome/browser/usb/web_usb_permission_provider.cc
index c0727eb1da6049b8832269728181063418eda0a2..2c23d2e2cc2db87bff8ffb060d48642799ec7d0f 100644
--- a/chrome/browser/usb/web_usb_permission_provider.cc
+++ b/chrome/browser/usb/web_usb_permission_provider.cc
@@ -11,6 +11,7 @@
 #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/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"
@@ -113,3 +114,19 @@ bool WebUSBPermissionProvider::HasFunctionPermission(
       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();
+}