[proxies] Better print for proxies in d8

src/d8.js

Index: src/d8.js
diff --git a/src/d8.js b/src/d8.js
index 8d55c788e2b42fa0d591ed146316c2c29dd9f365..c52d33a5f41f09ca33f048d32566519a363755b6 100644
--- a/src/d8.js
+++ b/src/d8.js
@@ -13,6 +13,9 @@ function Stringify(x, depth) {
     depth = stringifyDepthLimit;
   else if (depth === 0)
     return "*";
+  if (IS_PROXY(x)) {
+    return StringifyProxy(x, depth);
+  }
   switch (typeof x) {
     case "undefined":
       return "undefined";
@@ -63,3 +66,22 @@ function Stringify(x, depth) {
       return "[crazy non-standard value]";
   }
 }
+
+function StringifyProxy(proxy, depth) {
+  var proxy_type = typeof proxy;
+  return '[' + proxy_type + ' Proxy {' +
+    'target: ' +
+        StringifyProxyInternal(%JSProxyGetTarget(proxy), depth) + ', ' +
+    'handler: '+
+        StringifyProxyInternal(%JSProxyGetHandler(proxy), depth) +
+  '}]';
+}
+
+function StringifyProxyInternal(object, depth) {
+  // Special case to handle proxy __proto__ recursions on target or handler.
+  try {
+    return Stringify(object, depth-1);
+  } catch(RangeError) {
+    return '{*}'
+  }
+}