Lots of frog cleanup

frog/world.dart

Index: frog/world.dart
diff --git a/frog/world.dart b/frog/world.dart
index f41e934d29338a3a7b825a418cf8c95fcf953985..0e06f4130ebd96023ca062973f1a0b642649032b 100644
--- a/frog/world.dart
+++ b/frog/world.dart
@@ -406,6 +406,7 @@ class World {
     if (experimentalAwaitPhase != null) {
       withTiming('await translation', experimentalAwaitPhase);
     }
+    withTiming('analyze pass', () { analyzeCode(lib); });
     withTiming('generate code', () { generateCode(lib); });
   }
 
@@ -484,8 +485,18 @@ class World {
     return main;
   }
 
-  generateCode(Library lib) {
+  /**
+   * Walks all code in lib and imports for analysis.
+   */
+  analyzeCode(Library lib) {
     gen = new WorldGenerator(findMainMethod(lib), new CodeWriter());
+    gen.analyze();
+  }
+
+  /**
+   * Walks all live code to generate JS source for output.
+   */
+  generateCode(Library lib) {
     gen.run();
     frogCode = gen.writer.text;
     jsBytesWritten = frogCode.length;