Implement a list tracer phase, that tries to find element types in individual lists.

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

Index: sdk/lib/_internal/compiler/implementation/ssa/builder.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/ssa/builder.dart	(revision 24023)
+++ sdk/lib/_internal/compiler/implementation/ssa/builder.dart	(working copy)
@@ -3340,11 +3340,15 @@
       if (Elements.isFixedListConstructorCall(
               originalElement, send, compiler)) {
         isListConstructor = true;
-        return backend.fixedArrayType;
+        HType inferred =
+            new HType.inferredForNode(currentElement, node, compiler);
+        return inferred.isUnknown() ? backend.fixedArrayType : inferred;
       } else if (Elements.isGrowableListConstructorCall(
                     originalElement, send, compiler)) {
         isListConstructor = true;
-        return backend.extendableArrayType;
+        HType inferred =
+            new HType.inferredForNode(currentElement, node, compiler);
+        return inferred.isUnknown() ? backend.extendableArrayType : inferred;
       } else if (element.isGenerativeConstructor()) {
         ClassElement cls = element.getEnclosingClass();
         return new HType.nonNullExact(cls.thisType, compiler);
@@ -4102,7 +4106,10 @@
       visit(link.head);
       inputs.add(pop());
     }
-    push(buildLiteralList(inputs));
+    HInstruction instruction = buildLiteralList(inputs);
+    HType type = new HType.inferredForNode(currentElement, node, compiler);
+    if (!type.isUnknown()) instruction.instructionType = type;
+    push(instruction);
   }
 
   visitConditional(Conditional node) {