Add a fixed array type.

lib/compiler/implementation/ssa/optimize.dart

Index: lib/compiler/implementation/ssa/optimize.dart
===================================================================
--- lib/compiler/implementation/ssa/optimize.dart	(revision 13221)
+++ lib/compiler/implementation/ssa/optimize.dart	(working copy)
@@ -203,13 +203,8 @@
     // Try to recognize the length interceptor with input [:new List(int):].
     if (node.isLengthGetter() && node.inputs[1] is HInvokeStatic) {
       HInvokeStatic call = node.inputs[1];
-      Element element = call.target.element;
-      if (element.isConstructor() &&
-          element.enclosingElement.declaration ==
-              compiler.listClass.defaultClass.element) {
-        if (call.inputs.length == 2 && call.inputs[1].isInteger(types)) {
-          return call.inputs[1];
-        }
+      if (isFixedSizeListConstructor(call)) {
+        return call.inputs[1];
       }
     }
     HInstruction input = node.inputs[1];
@@ -251,6 +246,21 @@
     return node;
   }
 
+  bool isFixedSizeListConstructor(HInvokeStatic node) {
+    Element element = node.inputs[0].element;
+    return element.isConstructor()
+        && element.enclosingElement == compiler.listClass.defaultClass.element
+        && node.inputs.length == 2
+        && node.inputs[1].isInteger(types);
+  }
+
+  HInstruction visitInvokeStatic(HInvokeStatic node) {
+    if (isFixedSizeListConstructor(node)) {
+      node.guaranteedType = HType.FIXED_ARRAY;
+    }
+    return node;
+  }
+
   HInstruction visitInvokeDynamic(HInvokeDynamic node) {
     HType receiverType = types[node.receiver];
     if (receiverType.isExact()) {