[inspector] description for weak collections should not contain size

test/inspector/runtime/length-or-size-description.js

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 InspectorTest.log("Test that descriptions for arrays, maps, and sets include the correct length or size.")
 
 Promise.all([
   testExpression("new Set()"),
   testExpression("new Set([1,2])"),
   testExpression("new Map()"),
   testExpression("new Map([[1,2],[3,4]])"),
   testExpression("new Array()"),
   testExpression("new Array(2)"),
   testExpression("new Uint8Array()"),
-  testExpression("new Uint8Array(2)")
+  testExpression("new Uint8Array(2)"),
+  // WeakMap and WeakSet should not have size in description.
+  testExpression("new WeakMap([[{}, 42]])"),
+  testExpression("new WeakSet([{}])")
 ]).then(() => InspectorTest.completeTest());
 
 function testExpression(expression) {
   return Protocol.Runtime.evaluate({ expression: expression })
             .then(result => InspectorTest.logMessage(result.result.result.description))
             .then(() => Protocol.Runtime.evaluate({ expression: "[" + expression + "]", generatePreview: true }))
             .then(result => InspectorTest.logMessage(result.result.result.preview.properties[0].value))
 }