Fix UAF on libusb thread

device/usb/usb_context.cc

Index: device/usb/usb_context.cc
diff --git a/device/usb/usb_context.cc b/device/usb/usb_context.cc
index 99b76ab34be140118378b95d126891e4db480709..742b40d4517316f9e0421b1c1701c1e81f216602 100644
--- a/device/usb/usb_context.cc
+++ b/device/usb/usb_context.cc
@@ -61,9 +61,10 @@ void UsbContext::UsbEventHandler::ThreadMain() {
 }
 
 void UsbContext::UsbEventHandler::Stop() {
+  base::PlatformThreadHandle thread_handle = thread_handle_;
   base::subtle::Release_Store(&running_, 0);
   libusb_interrupt_handle_event(context_);

[Reilly Grant (use Gerrit), 2015/08/10 17:14:08]

context_ could also have been freed if there was another event that woke up the
thread and caused it to observe running_ == 0.

-  base::PlatformThread::Join(thread_handle_);
+  base::PlatformThread::Join(thread_handle);
 }
 
 UsbContext::UsbContext(PlatformUsbContext context) : context_(context) {