Port chromium landmines script.

DEPS

Index: DEPS
diff --git a/DEPS b/DEPS
index b829d05dabb9ad6e992719935c844d5f7aed8754..c46d1a240a69c4bffd1f8680de385c8a8b37a92d 100644
--- a/DEPS
+++ b/DEPS
@@ -46,6 +46,17 @@ skip_child_includes = [
 ]
 
 hooks = [
+  {
+    # This clobbers when necessary (based on get_landmines.py). It must be the
+    # first hook so that other things that get/generate into the output
+    # directory will not subsequently be clobbered.
+    'name': 'landmines',
+    'pattern': '.',
+    'action': [
+        'python',
+        'v8/build/landmines.py',
+    ],
+  },
   # Pull clang-format binaries using checked-in hashes.
   {
     "name": "clang_format_win",