Re-enable 4 canvas pixel tests.

  Pixel_Canvas2DRedBox
  Pixel_CanvasDisplayLinearRGBAccelerated2D
  Pixel_CanvasDisplayLinearRGBUnaccelerated2DGPUCompositing
  Pixel_CanvasLowLatency2D

Should be rebaselined at this point.

Bug: 918952
Change-Id: I89238fe4e294582e356ccfaf8b394b253f925976
Tbr: fserb@chromium.org
Tbr: mcasas@chromium.org
Tbr: zakerinasab@chromium.org
Tbr: ynovikov@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/c/1395003Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#620015}

content/test/gpu/gpu_tests/pixel_expectations.py

@@ -46,13 +46,6 @@ class PixelExpectations(GpuTestExpectations):
     self.Fail('Pixel_ScissorTestWithPreserveDrawingBuffer',
         ['android'], bug=521588)
 
-    # TODO(kbr): re-enable after rebaseline to clear up Nexus 5 failures
-    self.Fail('Pixel_Canvas2DRedBox', bug=918952)
-    self.Fail('Pixel_CanvasDisplayLinearRGBAccelerated2D', bug=918952)
-    self.Fail('Pixel_CanvasDisplayLinearRGBUnaccelerated2DGPUCompositing',
-              bug=918952)
-    self.Fail('Pixel_CanvasLowLatency2D', bug=918952)
-
     # TODO(vmiura) check / generate reference images for Android devices
     self.Fail('Pixel_SolidColorBackground', ['mac', 'android'], bug=624256)