Decompose //extensions/browser/BUILD.gn

extensions/browser/api/usb/BUILD.gn

Index: extensions/browser/api/usb/BUILD.gn
diff --git a/extensions/browser/api/usb/BUILD.gn b/extensions/browser/api/usb/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..8d2708e00c81641b43b2bf5436b9526df83ee088
--- /dev/null
+++ b/extensions/browser/api/usb/BUILD.gn
@@ -0,0 +1,22 @@
+# Copyright 2016 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.
+
+source_set("usb") {
+  sources = [
+    "usb_api.cc",
+    "usb_api.h",
+    "usb_device_resource.cc",
+    "usb_device_resource.h",
+    "usb_event_router.cc",
+    "usb_event_router.h",
+    "usb_guid_map.cc",
+    "usb_guid_map.h",
+  ]
+
+  deps = [
+    "//content/public/common",
+    "//extensions/common/api",
+    "//skia",
+  ]
+}