Add comment warning about modifying landmines

build/get_landmines.py

Index: build/get_landmines.py
diff --git a/build/get_landmines.py b/build/get_landmines.py
index 481240ffe316599f37be7003209298700c001ea1..481970058650ef5a91224b05503ea942f46535d1 100755
--- a/build/get_landmines.py
+++ b/build/get_landmines.py
@@ -28,6 +28,16 @@ def print_landmines():
   # need to be cleaned up. If you're writing a new CL that causes build
   # dependency problems, fix the dependency problems instead of adding a
   # landmine.
+  #
+  # Before adding or changing a landmine consider the consequences of doing so.
+  # Doing so will wipe out every output directory on every Chrome developer's
+  # machine. This can be particularly problematic on Windows where the directory
+  # deletion may well fail (locked files, command prompt in the directory,
+  # etc.), and generated .sln and .vcxproj files will be deleted.
+  #
+  # This output directory deletion will be repeated when going back and forth
+  # across the change that added the landmine, adding to the cost. There are
+  # usually less troublesome alternatives.

[(unused - use chromium), 2017/06/30 12:40:12]

I think the problem was that they didn't see the existing comment because it's
kind of at the top of this function, while people add stuff at the bottom. I
think maybe just moving this comment towards the bottom might be useful.

 
   if distributor() == 'goma' and platform() == 'win32':
     print 'Need to clobber winja goma due to backend cwd cache fix.'