Reland of Parse USB interface association descriptors.

device/usb/usb_descriptors.h

Index: device/usb/usb_descriptors.h
diff --git a/device/usb/usb_descriptors.h b/device/usb/usb_descriptors.h
index ba7169ae459a316aa15f40835042ef9560dc86bb..11b606ea9d91133fb29b2e9640b5e03e9d38807d 100644
--- a/device/usb/usb_descriptors.h
+++ b/device/usb/usb_descriptors.h
@@ -87,6 +87,8 @@ struct UsbInterfaceDescriptor {
   uint8_t interface_protocol;
   std::vector<UsbEndpointDescriptor> endpoints;
   std::vector<uint8_t> extra_data;
+  // First interface of the function to which this interface belongs.
+  uint8_t first_interface;
 };
 
 struct UsbConfigDescriptor {
@@ -98,6 +100,10 @@ struct UsbConfigDescriptor {
   UsbConfigDescriptor(const UsbConfigDescriptor& other);
   ~UsbConfigDescriptor();
 
+  // Scans through |extra_data| for interface association descriptors and
+  // populates |first_interface| for each interface in this configuration.
+  void AssignFirstInterfaceNumbers();
+
   uint8_t configuration_value;
   bool self_powered;
   bool remote_wakeup;