Added mock_xhr module w/ unit tests.

remoting/webapp/base/js/base_unittest.js

Index: remoting/webapp/base/js/base_unittest.js
diff --git a/remoting/webapp/base/js/base_unittest.js b/remoting/webapp/base/js/base_unittest.js
index c2812ad8a3361e772856bbf383f2b05ec65f32a3..afa7c825ce8f55e3ada69eb52f2b6f1120b04e11 100644
--- a/remoting/webapp/base/js/base_unittest.js
+++ b/remoting/webapp/base/js/base_unittest.js
@@ -54,6 +54,49 @@ QUnit.test('deepCopy(obj) should copy primitive types recursively',
     assert.deepEqual(base.deepCopy([1, [2, [3]]]), [1, [2, [3]]]);
 });
 
+QUnit.test('copyWithoutNullFields returns a new object',
+  function(assert) {
+    var obj = {
+      a: 'foo',
+      b: 42
+    };
+    var copy = base.copyWithoutNullFields(obj);
+    assert.notEqual(obj, copy);
+    assert.deepEqual(obj, copy);
+});
+
+QUnit.test('copyWithoutNullFields removes null and undefined fields',
+  function(assert) {
+    /** @const */
+    var obj = {
+      a: 'foo',
+      b: 42,
+      nullField: null,
+      undefinedField: undefined

[Jamie, 2015/04/03 01:45:57]

Add zero and '' fields to address my earlier comment.

[John Williams, 2015/04/04 01:40:25]

Done.

+    };
+    var copy = base.copyWithoutNullFields(obj);
+    assert.equal(copy['a'], obj['a']);
+    assert.equal(copy['b'], obj['b']);
+    assert.ok(!('nullField' in copy));
+    assert.ok(!('undefinedField' in copy));
+});
+
+QUnit.test('copyWithoutNullFields(null) returns a new empty bject',
+  function(assert) {
+    assert.deepEqual(
+        base.copyWithoutNullFields(null),
+        {});
+    assert.notEqual(
+        base.copyWithoutNullFields(null),
+        base.copyWithoutNullFields(null));
+    assert.deepEqual(
+        base.copyWithoutNullFields(undefined),
+        {});
+    assert.notEqual(
+        base.copyWithoutNullFields(undefined),
+        base.copyWithoutNullFields(undefined));
+});
+
 QUnit.test('modify the original after deepCopy(obj) should not affect the copy',
   function(assert) {
     var original = [1, 2, 3, 4];