Port chromium landmines script.

DEPS

 # Note: The buildbots evaluate this file with CWD set to the parent
 # directory and assume that the root of the checkout is in ./v8/, so
 # all paths in here must match this assumption.
 
 vars = {
   "git_url": "https://chromium.googlesource.com",
 }
 
 deps = {
   "v8/build/gyp":
@@ skipping 28 matching lines @@
   "+third_party/fdlibm",
 ]
 
 # checkdeps.py shouldn't check for includes in these directories:
 skip_child_includes = [
   "build",
   "third_party",
 ]
 
 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",
     "pattern": ".",
     "action": [ "download_from_google_storage",
                 "--no_resume",
                 "--platform=win32",
                 "--no_auth",
                 "--bucket", "chromium-clang-format",
                 "-s", "v8/buildtools/win/clang-format.exe.sha1",
@@ skipping 38 matching lines @@
     'name': 'clang',
     'pattern': '.',
     'action': ['python', 'v8/tools/clang/scripts/update.py', '--if-needed'],
   },
   {
     # A change to a .gyp, .gypi, or to GYP itself should run the generator.
     "pattern": ".",
     "action": ["python", "v8/build/gyp_v8"],
   },
 ]