Big merge from experimental to bleeding edge.

sdk/lib/_internal/compiler/implementation/js_backend/backend.dart

Index: sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart b/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
index e2c13472d37fa3771b0659581f297ec1a56d0beb..cd95643780ea9b3ca64ac2372f1b25fcb21da85b 100644
--- a/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
@@ -44,8 +44,8 @@ class OptionalParameterTypes {
   final List<HType> types;
 
   OptionalParameterTypes(int optionalArgumentsCount)
-      : names = new List<SourceString>(optionalArgumentsCount),
-        types = new List<HType>(optionalArgumentsCount);
+      : names = new List<SourceString>.fixedLength(optionalArgumentsCount),
+        types = new List<HType>.fixedLength(optionalArgumentsCount);
 
   int get length => names.length;
   SourceString name(int index) => names[index];
@@ -71,10 +71,10 @@ class HTypeList {
   final List<SourceString> namedArguments;
 
   HTypeList(int length)
-      : types = new List<HType>(length),
+      : types = new List<HType>.fixedLength(length),
         namedArguments = null;
   HTypeList.withNamedArguments(int length, this.namedArguments)
-      : types = new List<HType>(length);
+      : types = new List<HType>.fixedLength(length);
   const HTypeList.withAllUnknown()
       : types = null,
         namedArguments = null;