Frog shouldn't read libraries with --leg_only.

dart/frog/world.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.
 
 /** The one true [World]. */
 World world;
 
 /**
  * Experimental phase to enable await, only set when using the
  * await/awaitc.dart entrypoint.
@@ skipping 10 matching lines @@
 typedef void MessageHandler(String prefix, String message, SourceSpan span);
 
 
 /**
  * Should be called exactly once to setup singleton world.
  * Can use world.reset() to reinitialize.
  */
 void initializeWorld(FileSystem files) {
   assert(world == null);
   world = new World(files);
-  world.init();
+  if (!options.legOnly) world.init();
 }
 
 /**
  * Compiles the [target] dart file using the given [corelib].
  */
 bool compile(String homedir, List<String> args, FileSystem files) {
   parseOptions(homedir, args, files);
   initializeWorld(files);
   return world.compileAndSave();
 }
@@ skipping 17 matching lines @@
 
 /** Counters that track statistics about the generated code. */
 class CounterLog {
   int dynamicMethodCalls = 0;
   int typeAsserts = 0;
   int objectProtoMembers = 0;
   int invokeCalls = 0;
   int msetN = 0;
 
   info() {
+    if (options.legOnly) return;
     world.info('Dynamically typed method calls: $dynamicMethodCalls');
     world.info('Generated type assertions: $typeAsserts');
     world.info('Members on Object.prototype: $objectProtoMembers');
     world.info('Invoke calls: $invokeCalls');
     world.info('msetN calls: $msetN');
   }
 
   // We need to push a new counter when we are abstract interpreting, so we
   // can discard it if we discard the code.
   // TODO(jmesserly): this is ugly but I'm not sure how to make it cleaner,
@@ skipping 293 matching lines @@
   }
 
   bool compile() {
     // TODO(jimhug): Must have called setOptions - better errors.
     if (options.dartScript == null) {
       fatal('no script provided to compile');
       return false;
     }
 
     try {
-      info('compiling ${options.dartScript} with corelib $corelib');
+      if (options.legOnly) {
+        info('[leg] compiling ${options.dartScript}');
+      } else {
+        info('compiling ${options.dartScript} with corelib $corelib');
+      }
       if (!runLeg()) runCompilationPhases();
     } catch (var exc) {
       if (hasErrors && !options.throwOnErrors) {
         // TODO(jimhug): If dev mode then throw.
       } else {
         // TODO(jimhug): Handle these in world or in callers?
         throw;
       }
     }
     printStatus();
     return !hasErrors;
   }
 
   /** Returns true if Leg handled the compilation job. */
   bool runLeg() {
-    if (!options.enableLeg) return false;
+    if (!options.legOnly) return false;
     if (legCompile == null) {
       fatal('requested leg enabled, but no leg compiler available');
     }
-    bool res = withTiming('try leg compile', () => legCompile(this));
+    bool res = withTiming('[leg] compile', () => legCompile(this));
     if (!res && options.legOnly) {
       fatal("Leg could not compile ${options.dartScript}");
       return true; // In --leg_only, always "handle" the compilation.
     }
     return res;
   }
 
   void runCompilationPhases() {
     final lib = withTiming('first pass', () => processDartScript());
     withTiming('resolve top level', resolveAll);
     if (experimentalAwaitPhase != null) {
       withTiming('await translation', experimentalAwaitPhase);
     }
     withTiming('analyze pass', () { analyzeCode(lib); });
     if (options.checkOnly) return;
 
     withTiming('generate code', () { generateCode(lib); });
   }
 
   String getGeneratedCode() {
     // TODO(jimhug): Assert compilation is all done here.
     if (legCode != null) {
-      assert(options.enableLeg);
+      assert(options.legOnly);
       return legCode;
     } else {
       return frogCode;
     }
   }
 
   SourceFile readFile(String filename) {
     try {
       final sourceFile = reader.readFile(filename);
       dartBytesRead += sourceFile.text.length;
@@ skipping 190 matching lines @@
 
   withTiming(String name, f()) {
     final sw = new Stopwatch();
     sw.start();
     var result = f();
     sw.stop();
     info('$name in ${sw.elapsedInMs()}msec');
     return result;
   }
 }