Enable gyp_compare_flag_script to compare all targets.

tools/gyp_flag_compare.py

 #!/usr/bin/env python
 
 # Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 """Given the output of -t commands from a ninja build for a gyp and GN generated
 build, report on differences between the command lines.
 
 
 When invoked from the command line, this script assumes that the GN and GYP
 targets have been generated in the specified folders. It is meant to be used as
 follows:
   $ python tools/gyp_flag_compare.py gyp_dir gn_dir target
 
 When the GN and GYP target names differ, it should be called invoked as follows:
   $ python tools/gyp_flag_compare.py gyp_dir gn_dir gyp_target gn_target
 
+When all targets want to be compared, it should be called without a target name,
+i.e.:
+  $ python tools/gyp_flag_compare.py gyp_dir gn_dir
 
 This script can also be used interactively. Then ConfigureBuild can optionally
 be used to generate ninja files with GYP and GN.
 Here's an example setup. Note that the current working directory must be the
 project root:
   $ PYTHONPATH=tools python
   >>> import sys
   >>> import pprint
   >>> sys.displayhook = pprint.pprint
   >>> import gyp_flag_compare as fc
@@ skipping 73 matching lines @@
   for path in dict_of_list:
     dirname = os.path.dirname(path)
     r.setdefault(dirname, 0)
     r[dirname] += 1
   return r
 
 
 class Comparison(object):
   """A comparison of the currently-configured build for a target."""
 
-  def __init__(self, gyp_target, gn_target=None, gyp_dir=_DEFAULT_GYP_DIR,
+  def __init__(self, gyp_target="", gn_target=None, gyp_dir=_DEFAULT_GYP_DIR,
                gn_dir=_DEFAULT_GN_DIR):
     """Creates a comparison of a GN and GYP target. If the target names differ
     between the two build systems, then two names may be passed.
     """
     if gn_target is None:
       gn_target = gyp_target
     self._gyp_target = gyp_target
     self._gn_target = gn_target
 
     self._gyp_dir = gyp_dir
@@ skipping 255 matching lines @@
   return result
 
 
 def Run(command_line):
   """Run |command_line| as a subprocess and return stdout. Raises on error."""
   print >> sys.stderr, command_line
   return subprocess.check_output(command_line, shell=True)
 
 
 def main():
-  if len(sys.argv) < 4:
-    print 'usage: %s gyp_dir gn_dir target' % __file__
+  if len(sys.argv) < 3:
+    print 'usage: %s gyp_dir gn_dir' % __file__
+    print '   or: %s gyp_dir gn_dir target' % __file__
     print '   or: %s gyp_dir gn_dir gyp_target gn_target' % __file__
     return 1
 
   gyp_dir = sys.argv[1]
   gn_dir = sys.argv[2]
 
-  gyp_target = sys.argv[3]
-  if len(sys.argv) == 4:
-    gn_target = gyp_target
-  else:
+  gyp_target = gn_target = ""
+
+  if len(sys.argv) > 3:
+    gyp_target = sys.argv[3]
+  if len(sys.argv) > 4:
     gn_target = sys.argv[4]
 
   print 'GYP output directory is %s' % gyp_dir
   print 'GN output directory is %s' % gn_dir
 
   comparison = Comparison(gyp_target, gn_target, gyp_dir, gn_dir)
 
   gyp_files = comparison.gyp_files
   gn_files = comparison.gn_files
   different_source_list = comparison.gyp_files != comparison.gn_files
@@ skipping 28 matching lines @@
     print '\n'.join(sorted(files))
     print diff
 
   print 'Total differences:', comparison.total_differences
   # TODO(scottmg): Return failure on difference once we're closer to identical.
   return 0
 
 
 if __name__ == '__main__':
   sys.exit(main())