dart2js: Implement frequency based naming.

pkg/compiler/lib/src/apiimpl.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library leg_apiimpl;
 
 import 'dart:async';
 import 'dart:convert';
 
 import '../compiler.dart' as api;
@@ skipping 61 matching lines @@
             analyzeMain: hasOption(options, '--analyze-main'),
             analyzeSignaturesOnly:
                 hasOption(options, '--analyze-signatures-only'),
             strips: extractCsvOption(options, '--force-strip='),
             enableConcreteTypeInference:
                 hasOption(options, '--enable-concrete-type-inference'),
             disableTypeInferenceFlag:
                 hasOption(options, '--disable-type-inference'),
             preserveComments: hasOption(options, '--preserve-comments'),
             useCpsIr: hasOption(options, '--use-cps-ir'),
+            useFrequencyNamer: hasOption(options, "--use-frequency-naming"),

[sra1, 2015/07/01 04:11:09]

Maybe move this next to --minify since that is what it modifies.
Pick a name relates it to minified code, e.g.  --minify-by-frequency

[herhut, 2015/07/02 08:54:51]

After talking to floitsch@, I have now enabled frequency based naming by default
and added --no-frequency-based-minification to enable the old behavior.

             verbose: hasOption(options, '--verbose'),
             sourceMapUri: extractUriOption(options, '--source-map='),
             outputUri: extractUriOption(options, '--out='),
             terseDiagnostics: hasOption(options, '--terse'),
             deferredMapUri: extractUriOption(options, '--deferred-map='),
             dumpInfo: hasOption(options, '--dump-info'),
             buildId: extractStringOption(
                 options, '--build-id=',
                 "build number could not be determined"),
             showPackageWarnings:
@@ skipping 377 matching lines @@
     print('$message: ${tryToString(exception)}');
     print(tryToString(stackTrace));
   }
 
   fromEnvironment(String name) => environment[name];
 
   LibraryInfo lookupLibraryInfo(String libraryName) {
     return library_info.LIBRARIES[libraryName];
   }
 }