Reenable and strengthen screenshot_sync test.

content/test/gpu/gpu_tests/screenshot_sync.py

Index: content/test/gpu/gpu_tests/screenshot_sync.py
diff --git a/content/test/gpu/gpu_tests/screenshot_sync.py b/content/test/gpu/gpu_tests/screenshot_sync.py
index caa38532119b10674f379ee5ac87956996343374..cce1730660368ca0fef202dfe2b9fe03532e1177 100644
--- a/content/test/gpu/gpu_tests/screenshot_sync.py
+++ b/content/test/gpu/gpu_tests/screenshot_sync.py
@@ -11,6 +11,7 @@ from gpu_tests import screenshot_sync_expectations
 from telemetry.page import page_test
 from telemetry.story import story_set as story_set_module
 from telemetry.util import image_util
+from telemetry.util import rgba_color
 
 data_path = os.path.join(
     path_util.GetChromiumSrcDir(), 'content', 'test', 'data', 'gpu')
@@ -26,31 +27,42 @@ class ScreenshotSyncValidator(gpu_test_base.ValidatorBase):
     if not tab.screenshot_supported:
       raise page_test.Failure('Browser does not support screenshot capture')
 
-    def CheckColorMatch(canvasRGB, screenshotRGB):
-      for i in range(0, 3):
-        if abs(canvasRGB[i] - screenshotRGB[i]) > 1:
-          raise page_test.Failure('Color mismatch in component #%d: %d vs %d' %
-              (i, canvasRGB[i], screenshotRGB[i]))
+    def CheckColorMatchAtLocation(expectedRGB, screenshot, x, y):
+      pixel_value = image_util.GetPixelColor(screenshot, x, y)
+      if not expectedRGB.IsEqual(pixel_value):
+        error_message = ('Color mismatch at (%d, %d): expected (%d, %d, %d), ' +
+                         'got (%d, %d, %d)') % (
+                             x, y, expectedRGB.r, expectedRGB.g, expectedRGB.b,
+                             pixel_value.r, pixel_value.g, pixel_value.b)
+        raise page_test.Failure(error_message)
 
     def CheckScreenshot():
-      canvasRGB = []
-      for _ in range(0, 3):
-        canvasRGB.append(random.randint(0, 255))
-      tab.EvaluateJavaScript("window.draw(%d, %d, %d);" % tuple(canvasRGB))
+      canvasRGB = rgba_color.RgbaColor(random.randint(0, 255),
+                                       random.randint(0, 255),
+                                       random.randint(0, 255),
+                                       255)
+      tab.EvaluateJavaScript("window.draw(%d, %d, %d);" % (
+          canvasRGB.r, canvasRGB.g, canvasRGB.b))
       screenshot = tab.Screenshot(5)
-      CheckColorMatch(canvasRGB, image_util.Pixels(screenshot))
+      start_x = 10
+      start_y = 0
+      outer_size = 256
+      skip = 10
+      for y in range(start_y, outer_size, skip):
+        for x in range(start_x, outer_size, skip):
+          CheckColorMatchAtLocation(canvasRGB, screenshot, x, y)
 
-    repetitions = 50
+    repetitions = 20
     for _ in range(0, repetitions):
       CheckScreenshot()
 
 class ScreenshotSyncPage(gpu_test_base.PageBase):
-  def __init__(self, story_set, base_dir, expectations):
+  def __init__(self, story_set, base_dir, url, name, expectations):
     super(ScreenshotSyncPage, self).__init__(
-      url='file://screenshot_sync.html',
+      url=url,
       page_set=story_set,
       base_dir=base_dir,
-      name='ScreenshotSync',
+      name=name,
       expectations=expectations)
 
 
@@ -68,5 +80,12 @@ class ScreenshotSyncProcess(gpu_test_base.TestBase):
 
   def CreateStorySet(self, options):
     ps = story_set_module.StorySet(base_dir=data_path, serving_dirs=[''])
-    ps.AddStory(ScreenshotSyncPage(ps, ps.base_dir, self.GetExpectations()))
+    ps.AddStory(ScreenshotSyncPage(ps, ps.base_dir,
+                                   'file://screenshot_sync_canvas.html',
+                                   'ScreenshotSync.WithCanvas',
+                                   self.GetExpectations()))
+    ps.AddStory(ScreenshotSyncPage(ps, ps.base_dir,
+                                   'file://screenshot_sync_divs.html',
+                                   'ScreenshotSync.WithDivs',
+                                   self.GetExpectations()))
     return ps