Start work on a non-complete type inferrer. Currently only analyzes return types.

sdk/lib/_internal/compiler/implementation/ssa/types.dart

Index: sdk/lib/_internal/compiler/implementation/ssa/types.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/ssa/types.dart	(revision 18311)
+++ sdk/lib/_internal/compiler/implementation/ssa/types.dart	(working copy)
@@ -26,18 +26,28 @@
           isInterfaceType: isInterfaceType);
     }
 
-    if (element == compiler.intClass) {
+    JavaScriptBackend backend = compiler.backend;
+    if (element == compiler.intClass || element == backend.jsIntClass) {
       return canBeNull ? HType.INTEGER_OR_NULL : HType.INTEGER;
-    } else if (element == compiler.numClass) {
+    } else if (element == compiler.numClass 
+               || element == backend.jsNumberClass) {
       return canBeNull ? HType.NUMBER_OR_NULL : HType.NUMBER;
-    } else if (element == compiler.doubleClass) {
+    } else if (element == compiler.doubleClass
+               || element == backend.jsDoubleClass) {
       return canBeNull ? HType.DOUBLE_OR_NULL : HType.DOUBLE;
-    } else if (element == compiler.stringClass) {
+    } else if (element == compiler.stringClass
+               || element == backend.jsStringClass) {
       return canBeNull ? HType.STRING_OR_NULL : HType.STRING;
-    } else if (element == compiler.boolClass) {
+    } else if (element == compiler.boolClass
+               || element == backend.jsBoolClass) {
       return canBeNull ? HType.BOOLEAN_OR_NULL : HType.BOOLEAN;
-    } else if (element == compiler.nullClass) {
+    } else if (element == compiler.nullClass
+               || element == backend.jsNullClass) {
       return HType.NULL;
+    } else if (element == backend.jsArrayClass) {
+      return canBeNull
+          ? HType.READABLE_ARRAY.union(HType.NULL)
+          : HType.READABLE_ARRAY;
     } else if (!isExact) {
       if (element == compiler.listClass
           || Elements.isListSupertype(element, compiler)) {