Finish strong mode cleaning of dart2js.

pkg/compiler/lib/src/types/union_type_mask.dart

Index: pkg/compiler/lib/src/types/union_type_mask.dart
diff --git a/pkg/compiler/lib/src/types/union_type_mask.dart b/pkg/compiler/lib/src/types/union_type_mask.dart
index 2832b75e8cb508ec5969ad5411f2179216546dc6..1997d0275502b1d187f8f24159ad7ce82539da9f 100644
--- a/pkg/compiler/lib/src/types/union_type_mask.dart
+++ b/pkg/compiler/lib/src/types/union_type_mask.dart
@@ -96,7 +96,7 @@ class UnionTypeMask implements TypeMask {
     bool useSubclass = masks.every((e) => !e.isSubtype);
     bool isNullable = masks.any((e) => e.isNullable);
 
-    List masksBases = masks.map((mask) => mask.base).toList();
+    List<ClassEntity> masksBases = masks.map((mask) => mask.base).toList();
     Iterable<ClassEntity> candidates =
         closedWorld.commonSupertypesOf(masksBases);
 
@@ -137,7 +137,7 @@ class UnionTypeMask implements TypeMask {
     return new TypeMask(bestElement, bestKind, isNullable, closedWorld);
   }
 
-  TypeMask union(var other, ClosedWorld closedWorld) {
+  TypeMask union(dynamic other, ClosedWorld closedWorld) {
     other = TypeMask.nonForwardingMask(other);
     if (!other.isUnion && disjointMasks.contains(other)) return this;
 
@@ -151,7 +151,7 @@ class UnionTypeMask implements TypeMask {
     return new TypeMask.unionOf(newList, closedWorld);
   }
 
-  TypeMask intersection(var other, ClosedWorld closedWorld) {
+  TypeMask intersection(dynamic other, ClosedWorld closedWorld) {
     other = TypeMask.nonForwardingMask(other);
     if (!other.isUnion && disjointMasks.contains(other)) return other;
     if (other.isUnion && this == other) return this;