[mojo] Import and use own copy of V8's concatenate_files.py

V8 will shortly drop this script. Import our own copy in
mojo/public/tools/ and use that for mojo's build.

The concatenate-files.py script is copied, modulo license header, from
V8's tools/ directory.

Bug: v8:7624
Change-Id: I07c6a64f061c3957002ca6f2c83c7f93b3ec009d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1845764Reviewed-by: Oksana Zhuravlova <oksamyt@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#704237}

mojo/public/js/BUILD.gn

@@ -38,7 +38,7 @@ action("bindings") {
 
   # TODO(yzshen): Eventually we would like to use Closure Compiler to minify the
   # bindings instead of simply concatenating the files.
-  script = "//v8/tools/concatenate-files.py"
+  script = "//mojo/public/tools/bindings/concatenate-files.py"
 
   sources = bindings_js_files
   outputs = [

mojo/public/tools/bindings/concatenate-files.py

+#!/usr/bin/env python
+# Copyright 2019 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+#
+# This utility concatenates several files into one. On Unix-like systems
+# it is equivalent to:
+#   cat file1 file2 file3 ...files... > target
+#
+# The reason for writing a separate utility is that 'cat' is not available
+# on all supported build platforms, but Python is, and hence this provides
+# us with an easy and uniform way of doing this on all platforms.
+
+# for py2/py3 compatibility
+from __future__ import print_function
+
+import optparse
+
+
+def Concatenate(filenames):
+  """Concatenate files.
+
+  Args:
+    files: Array of file names.
+           The last name is the target; all earlier ones are sources.
+
+  Returns:
+    True, if the operation was successful.
+  """
+  if len(filenames) < 2:
+    print("An error occurred generating %s:\nNothing to do." % filenames[-1])
+    return False
+
+  try:
+    with open(filenames[-1], "wb") as target:
+      for filename in filenames[:-1]:
+        with open(filename, "rb") as current:
+          target.write(current.read())
+    return True
+  except IOError as e:
+    print("An error occurred when writing %s:\n%s" % (filenames[-1], e))
+    return False
+
+
+def main():
+  parser = optparse.OptionParser()
+  parser.set_usage("""Concatenate several files into one.
+      Equivalent to: cat file1 ... > target.""")
+  (_options, args) = parser.parse_args()
+  exit(0 if Concatenate(args) else 1)
+
+
+if __name__ == "__main__":
+  main()