Merge the work on Generic Types Reification from 'dart-lang/reify' repo

pkg/kernel/lib/target/vm.dart

Index: pkg/kernel/lib/target/vm.dart
diff --git a/pkg/kernel/lib/target/vm.dart b/pkg/kernel/lib/target/vm.dart
index 1366cae89f9e141531037064d183179c105de028..ed225449dd95610b8939b2bdcce16e0e4366092d 100644
--- a/pkg/kernel/lib/target/vm.dart
+++ b/pkg/kernel/lib/target/vm.dart
@@ -74,13 +74,7 @@ class VmTarget extends Target {
     }
 
     if (flags.treeShake) {
-      new TreeShaker(program,
-              hierarchy: _hierarchy,
-              coreTypes: coreTypes,
-              strongMode: strongMode,
-              programRoots: flags.programRoots)
-          .transform(program);
-      _hierarchy = null; // Hierarchy must be recomputed.
+      performTreeShaking(program);
     }
 
     cont.transformProgram(program);
@@ -94,4 +88,15 @@ class VmTarget extends Target {
 
     new SanitizeForVM().transform(program);
   }
+
+  void performTreeShaking(Program program) {
+    var coreTypes = new CoreTypes(program);
+    new TreeShaker(program,
+        hierarchy: _hierarchy,
+        coreTypes: coreTypes,
+        strongMode: strongMode,
+        programRoots: flags.programRoots)
+        .transform(program);
+    _hierarchy = null; // Hierarchy must be recomputed.
+  }
 }