gclient conditionals are supposed to allow '!=', but don't currently.

R=smut@chromium.org
TBR=phajdan.jr@chromium.org
BUG=570091

Change-Id: I9e0cce71105e9b819019d64c8857c2e86796a16f
Reviewed-on: https://chromium-review.googlesource.com/704224
Commit-Queue: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: smut <smut@google.com>

gclient_eval.py

@@ -306,6 +306,8 @@ def EvaluateCondition(condition, variables, referenced_variables=None):
 
       if isinstance(node.ops[0], ast.Eq):
         return left == right
+      if isinstance(node.ops[0], ast.NotEq):
+        return left != right
 
       raise ValueError(
           'unexpected operator: %s %s (inside %r)' % (

tests/gclient_eval_unittest.py

@@ -142,9 +142,17 @@ class EvaluateConditionTest(unittest.TestCase):
         'a or b', {'a': 'b and c', 'b': 'not c', 'c': 'False'}))
 
   def test_string_equality(self):
+    self.assertTrue(gclient_eval.EvaluateCondition(
+        'foo == "baz"', {'foo': '"baz"'}))
     self.assertFalse(gclient_eval.EvaluateCondition(
         'foo == "bar"', {'foo': '"baz"'}))
 
+  def test_string_inequality(self):
+    self.assertTrue(gclient_eval.EvaluateCondition(
+        'foo != "bar"', {'foo': '"baz"'}))
+    self.assertFalse(gclient_eval.EvaluateCondition(
+        'foo != "baz"', {'foo': '"baz"'}))
+
   def test_string_bool(self):
     self.assertFalse(gclient_eval.EvaluateCondition(
         'false_str_var and true_var',