Various caches for incremental compilation.

dart/sdk/lib/_internal/compiler/implementation/world.dart

Index: dart/sdk/lib/_internal/compiler/implementation/world.dart
diff --git a/dart/sdk/lib/_internal/compiler/implementation/world.dart b/dart/sdk/lib/_internal/compiler/implementation/world.dart
index ae56485644495ad46bb80e07ff225dc56c4fa746..4d1b07804756ad7d04fc9dc452432dd6f53fc8d9 100644
--- a/dart/sdk/lib/_internal/compiler/implementation/world.dart
+++ b/dart/sdk/lib/_internal/compiler/implementation/world.dart
@@ -32,6 +32,8 @@ class World {
   final Set<Element> functionsThatMightBePassedToApply =
       new Set<FunctionElement>();
 
+  final Set<Element> alreadyPopulated = new Set<Element>.identity();
+
   Set<ClassElement> subclassesOf(ClassElement cls) {
     return _subclasses[cls.declaration];
   }
@@ -59,6 +61,9 @@ class World {
 
   void populate() {
     void addSubtypes(ClassElement cls) {
+      if (compiler.hasIncrementalSupport && !alreadyPopulated.add(cls)) {
+        return;
+      }
       assert(cls.isDeclaration);
       if (cls.resolutionState != STATE_DONE) {
         compiler.internalError(cls, 'Class "${cls.name}" is not resolved.');