Enable pixel tests for low latency canvas

BUG=788439
TBR=zmo@chromium.org

Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Change-Id: Ib758904323adb6039d21f916d4aed9fdc631278e
Reviewed-on: https://chromium-review.googlesource.com/1144275
Commit-Queue: Justin Novosad <junov@chromium.org>
Reviewed-by: Justin Novosad <junov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576759}

content/test/gpu/gpu_tests/pixel_expectations.py

@@ -63,12 +63,6 @@ class PixelExpectations(GpuTestExpectations):
     self.Fail('Pixel_OffscreenCanvasUnaccelerated2DGPUCompositingWorker',
               ['mac', 'linux', 'win', 'android', 'chromeos'], bug=788439)
 
-    # TODO(junov); validate new test results
-    self.Fail('Pixel_CanvasLowLatency2D',
-        ['mac', 'linux', 'win', 'android', 'chromeos'], bug=788439)
-    self.Fail('Pixel_CanvasUnacceleratedLowLatency2D',
-        ['mac', 'linux', 'win', 'android', 'chromeos'], bug=788439)
-
     # Flaky for unknown reasons only on macOS. Not planning to investigate
     # further.
     self.Flaky('Pixel_ScissorTestWithPreserveDrawingBuffer', ['mac'],