Fix generate_emma_html.py failing due to 0-length .em files

build/android/generate_emma_html.py

 #!/usr/bin/env python
 
 # Copyright 2013 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.
 
 """Aggregates EMMA coverage files to produce html output."""
 
 import fnmatch
 import json
@@ skipping 40 matching lines @@
                                  'runtime.'))
   options, _ = option_parser.parse_args()
 
   devil_chromium.Initialize()
 
   if not (options.coverage_dir and options.metadata_dir and options.output):
     option_parser.error('One or more mandatory options are missing.')
 
   coverage_files = _GetFilesWithExt(options.coverage_dir, 'ec')
   metadata_files = _GetFilesWithExt(options.metadata_dir, 'em')
+  # Filter out zero-length files. These are created by emma_instr.py when a
+  # target has no classes matching the coverage filter.
+  metadata_files = [f for f in metadata_files if os.path.getsize(f)]
   print 'Found coverage files: %s' % str(coverage_files)
   print 'Found metadata files: %s' % str(metadata_files)
 
   sources = []
   for f in metadata_files:
     sources_file = os.path.splitext(f)[0] + '_sources.txt'
     with open(sources_file, 'r') as sf:
       sources.extend(json.load(sf))
   sources = [os.path.join(host_paths.DIR_SOURCE_ROOT, s) for s in sources]
   print 'Sources: %s' % sources
 
   input_args = []
   for f in coverage_files + metadata_files:
     input_args.append('-in')
     input_args.append(f)
 
   output_args = ['-Dreport.html.out.file', options.output]
   source_args = ['-sp', ','.join(sources)]
 
   exit_code = cmd_helper.RunCmd(
       ['java', '-cp',
        os.path.join(constants.ANDROID_SDK_ROOT, 'tools', 'lib', 'emma.jar'),
        'emma', 'report', '-r', 'html']
       + input_args + output_args + source_args)
 
   if options.cleanup:
     for f in coverage_files:
       os.remove(f)
 
+  # Command tends to exit with status 0 when it actually failed.
+  if not exit_code and not os.path.exists(options.output):
+    exit_code = 1
+
   return exit_code
 
 
 if __name__ == '__main__':
   sys.exit(main())