Use depfiles for mojom generation.

mojo/public/tools/bindings/mojom_bindings_generator.py

Index: mojo/public/tools/bindings/mojom_bindings_generator.py
diff --git a/mojo/public/tools/bindings/mojom_bindings_generator.py b/mojo/public/tools/bindings/mojom_bindings_generator.py
index 78af6499de564493eedd164e091d74b3cd0f428c..3a0b6fc87e25f23febb0e6ff049728f6013fcb42 100755
--- a/mojo/public/tools/bindings/mojom_bindings_generator.py
+++ b/mojo/public/tools/bindings/mojom_bindings_generator.py
@@ -236,6 +236,12 @@ def _Generate(args, remaining_args):
   processor.LoadTypemaps(set(args.typemaps))
   for filename in args.filename:
     processor.ProcessFile(args, remaining_args, generator_modules, filename)
+  if args.depfile:
+    assert args.depfile_target
+    with open(args.depfile, 'w') as f:
+      f.write('%s: %s' % (
+          args.depfile_target,
+          ' '.join(processor._parsed_files.keys())))
 
   return 0
 
@@ -302,6 +308,12 @@ def main():
   generate_parser.add_argument(
       "--generate_non_variant_code", action="store_true",
       help="Generate code that is shared by different variants.")
+  generate_parser.add_argument(
+      "--depfile", type=str,
+      help="A file into which the list of input files will be written.")
+  generate_parser.add_argument(
+      "--depfile_target", type=str,
+      help="The target name to use in the depfile.")
   generate_parser.set_defaults(func=_Generate)
 
   precompile_parser = subparsers.add_parser("precompile",