Auto-updating script for Windows toolchain

DEPS

Index: DEPS
diff --git a/DEPS b/DEPS
index ec52e306f9cb2143978e813017279a196b524c70..d4444f450c40511e7f84d5ecfaa308c675b4de4d 100644
--- a/DEPS
+++ b/DEPS
@@ -641,6 +641,14 @@ hooks = [
                "-s", "src/third_party/WebKit",
                "-o", "src/build/util/LASTCHANGE.blink"],
   },
+  # Windows toolchain setup.
+  {
+    "name": "toolchain_win",
+    "pattern": "\\.sha1$",
+    "action": [ "python",
+                "src/tools/win/toolchain/get_toolchain_if_necessary.py",
+    ],
+  },
   # Pull GN binaries. This needs to be before running GYP below.
   {
     "name": "gn_win",