Allow masks to be created from one image.

Modify image_tools to allow lists of one image to be used
to create a mask.

BUG=None
NOTRY=True

Review URL: https://codereview.chromium.org/98563005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238995 0039d316-1c4b-4281-b951-d872f2087c98

chrome/test/functional/ispy/common/image_tools.py

@@ -87,18 +87,18 @@ def CreateMask(images):
   everywhere else.
 
   Args:
-    images: the images to compute the mask from.
+    images: list of images to compute the mask from.
 
   Returns:
     an image of only black and white pixels where white pixels represent
       areas in the input images that have differences.
 
   Raises:
     Exception: if the images passed in are not of the same size.
-    Exception: if fewer than two images are passed in.
+    Exception: if fewer than one image is passed in.
   """
-  if len(images) < 2:
-    raise Exception('mask must be created from two or more images.')
+  if not images:
+    raise Exception('mask must be created from one or more images.')
   mask = Image.new('RGBA', images[0].size, (0, 0, 0, 255))
   image = images[0]
   for other_image in images[1:]:

chrome/test/functional/ispy/common/ispy_utils_unittest.py

@@ -79,6 +79,7 @@ def testGenerateExpectation(self):
     # Upload some tests to the datastore.
     self.ispy_utils.GenerateExpectation('test', [self.white, self.black])
     self.ispy_utils.GenerateExpectation('test1', [self.black, self.black])
+    self.ispy_utils.GenerateExpectation('test2', [self.black])
     # Confirm that the tests were successfully uploaded.
     self.assertEquals(self.bucket.datastore[
         ispy_utils.GetExpectationPath('test', 'expected.png')],
@@ -92,6 +93,12 @@ def testGenerateExpectation(self):
     self.assertEquals(self.bucket.datastore[
         ispy_utils.GetExpectationPath('test1', 'mask.png')],
         image_tools.EncodePNG(self.black))
+    self.assertEquals(self.bucket.datastore[
+        ispy_utils.GetExpectationPath('test2', 'expected.png')],
+        image_tools.EncodePNG(self.black))
+    self.assertEquals(self.bucket.datastore[
+        ispy_utils.GetExpectationPath('test2', 'mask.png')],
+        image_tools.EncodePNG(self.black))
 
   def testPerformComparison(self):
     self.bucket.Reset()