Misc clean-up of TabCaptureApiTests; and re-enable more tests.

chrome/test/data/extensions/api_test/tab_capture/constraints.js

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 chrome.test.runTests([
   function supportsMediaConstraints() {
     chrome.tabCapture.capture({
       video: true,
       audio: true,
       videoConstraints: {
           mandatory: {
             maxWidth: 1000,
             minWidth: 300
           }
       }
     }, function(stream) {
       chrome.test.assertTrue(!!stream);
       stream.stop();
       chrome.test.succeed();
     });
   },
 
-  function supportsOptionalMediaConstraints() {
+  function rejectsOptionalMediaConstraints() {
     chrome.tabCapture.capture({
       video: true,
       audio: true,
       videoConstraints: {
         mandatory: {
         },
         optional: {
           maxWidth: 1000,
           minWidth: 300
         }
       }
     }, function(stream) {
       chrome.test.assertTrue(!stream);
       chrome.test.succeed();
     });
+  },
+
+  function rejectsInvalidConstraints() {
+    chrome.tabCapture.capture({
+      video: true,
+      audio: true,
+      videoConstraints: {
+        mandatory: {
+          notValid: '123'
+        }
+      }
+    }, function(stream) {
+      chrome.test.assertTrue(!stream);
+
+      chrome.tabCapture.capture({

[miu, 2014/11/19 01:15:54]

This is the second test from api_tests_audio.js, which I expanded and cleaned up
further here.

+        audio: true,
+        audioConstraints: {
+          mandatory: {
+            notValid: '123'
+          }
+        }
+      }, function(stream) {
+        chrome.test.assertTrue(!stream);
+        chrome.test.succeed();
+      });
+    });
   }
 ]);