DEPS for gn, used by 'gclient runhooks' to sync gn in buildtools/.

DEPS

Index: DEPS
diff --git a/DEPS b/DEPS
index 6b2f7679939d771e5aef0e04d5e345b0929c82a0..f15a8f88dd49b5bb4bb944ce67154ab374982a89 100644
--- a/DEPS
+++ b/DEPS
@@ -136,6 +136,40 @@ hooks = [
                 '-d', 'v8/tools/luci-go/linux64',
     ],
   },
+  # Pull GN using checked-in hashes.
+  {
+    "name": "gn_win",
+    "pattern": ".",
+    "action": [ "download_from_google_storage",
+                "--no_resume",
+                "--platform=win32",
+                "--no_auth",
+                "--bucket", "chromium-gn",
+                "-s", "v8/buildtools/win/gn.exe.sha1",
+    ],
+  },
+  {
+    "name": "gn_mac",
+    "pattern": ".",
+    "action": [ "download_from_google_storage",
+                "--no_resume",
+                "--platform=darwin",
+                "--no_auth",
+                "--bucket", "chromium-gn",
+                "-s", "v8/buildtools/mac/gn.sha1",
+    ],
+  },
+  {
+    "name": "gn_linux",
+    "pattern": ".",
+    "action": [ "download_from_google_storage",
+                "--no_resume",
+                "--platform=linux*",
+                "--no_auth",
+                "--bucket", "chromium-gn",
+                "-s", "v8/buildtools/linux64/gn.sha1",
+    ],
+  },
   {
     # Update the Windows toolchain if necessary.
     'name': 'win_toolchain',