[win_toolchain] Add DIR_METADATA

This should route crash reports (e.g. https://crbug.com/1451128) to the
right component.

Fixed: b/285971982
Change-Id: If3391e4fb2b7af4f9fe91261283e8ef79a9e6759
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5141486
Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Auto-Submit: Josip Sokcevic <sokcevic@chromium.org>
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>

win_toolchain/DIR_METADATA

@@ -0,0 +1,3 @@
+monorail: {
+  component: "Build"
+}