Move main and isolate handling to enqueuer listeners.

pkg/compiler/lib/src/common_elements.dart

Index: pkg/compiler/lib/src/common_elements.dart
diff --git a/pkg/compiler/lib/src/common_elements.dart b/pkg/compiler/lib/src/common_elements.dart
index f69355d1a985953f0a0af759ee076ac1b20fb2e2..19cfb0e1d0c534240a1077c9003d46b7f9c3e89e 100644
--- a/pkg/compiler/lib/src/common_elements.dart
+++ b/pkg/compiler/lib/src/common_elements.dart
@@ -211,6 +211,14 @@ abstract class CommonElements {
 /// The environment makes private and injected members directly available and
 /// should therefore not be used to determine scopes.
 abstract class ElementEnvironment {
+  /// Returns the main library for the compilation.
+  LibraryEntity get mainLibrary;
+
+  /// Returns the main method for the compilation.
+  FunctionEntity get mainFunction;
+
+  /// Lookup the library with the canonical [uri], fail if the library is
+  /// missing and [required];
   LibraryEntity lookupLibrary(Uri uri, {bool required: false});
 
   /// Lookup the class [name] in [library], fail if the class is missing and