Add a few microbenchmarks for property caching

tests/perf/test-prop-read-long-inherit.js

@@ -0,0 +1,20 @@
+function test() {
+    var i;
+    var obj;
+
+    obj = { foo: 123 };
+    for (i = 0; i < 100; i++) {
+        obj = Object.create(obj);
+    }
+
+    for (i = 0; i < 1e7; i++) {
+        void obj.foo;
+    }
+}
+
+try {
+    test();
+} catch (e) {
+    print(e.stack || e);
+    throw e;
+}

tests/perf/test-prop-read-math-pi.js

@@ -0,0 +1,14 @@
+function test() {
+    var i;
+
+    for (i = 0; i < 1e7; i++) {
+        void Math.PI
+    }
+}
+
+try {
+    test();
+} catch (e) {
+    print(e.stack || e);
+    throw e;
+}

tests/perf/test-prop-write-long-inherit.js

@@ -0,0 +1,23 @@
+function test() {
+    var i;
+    var obj;
+
+    obj = { foo: 123 };
+    for (i = 0; i < 100; i++) {
+        obj = Object.create(obj);
+    }
+
+    for (i = 0; i < 1e7; i++) {
+        // Because a write always causes an own property to be created,
+        // there's no difference between a shallow and deep object except
+        // on the very first write.
+        obj.foo = 123;
+    }
+}
+
+try {
+    test();
+} catch (e) {
+    print(e.stack || e);
+    throw e;
+}