Implement get trap for proxies.

src/runtime.js

Index: src/runtime.js
diff --git a/src/runtime.js b/src/runtime.js
index 77b97aed837d654f8f8a3fda74cce5393674c25b..66e1661b759cc6ed66888d0f69d5cee4f9e3b6f6 100644
--- a/src/runtime.js
+++ b/src/runtime.js
@@ -647,3 +647,20 @@ function DefaultString(x) {
 // that is cloned when running the code.  It is essential that the
 // boilerplate gets the right prototype.
 %FunctionSetPrototype($Array, new $Array(0));
+
+
+/* ------------------------------------------
+- - -   H a r m o n y   P r o x i e s   - - -
+---------------------------------------------
+*/
+
+function DERIVED_GET_TRAP(receiver, name) {
+  var desc = this.getPropertyDescriptor(name);
+  if (IS_UNDEFINED(desc)) { return desc; }
+  if ('value' in desc) {
+    return desc.value;
+  } else {
+    if (IS_UNDEFINED(desc.get)) { return desc.get; }
+    return desc.get().call(receiver);  // The proposal says so...
+  }
+}