Remove fuzziness from MaskOfLayerWithBackdropFilter test

This test is really fuzzy when it doesn't need to be, allowing for
fairly large error when all of the test cases match it exactly. Remove
the fuzziness.

Bug: 948128
Change-Id: I1101377700def57816f7479e139c4804ffe8aa0a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1637397Reviewed-by: kylechar <kylechar@chromium.org>
Commit-Queue: Sean Gilhuly <sgilhuly@chromium.org>
Cr-Commit-Position: refs/heads/master@{#664821}

cc/trees/layer_tree_host_pixeltest_masks.cc

@@ -862,19 +862,6 @@ TEST_P(LayerTreeHostMasksForBackdropFiltersPixelTest,
   blur->SetMaskLayer(mask.get());
   CHECK_EQ(Layer::LayerMaskType::SINGLE_TEXTURE_MASK, mask->mask_type());
 
-  float percentage_pixels_large_error = 2.5f;  // 2.5%, ~250px / (100*100)
-  float percentage_pixels_small_error = 0.0f;
-  float average_error_allowed_in_bad_pixels = 100.0f;
-  int large_error_allowed = 256;
-  int small_error_allowed = 0;
-  pixel_comparator_ = std::make_unique<FuzzyPixelComparator>(
-      true,  // discard_alpha
-      percentage_pixels_large_error,
-      percentage_pixels_small_error,
-      average_error_allowed_in_bad_pixels,
-      large_error_allowed,
-      small_error_allowed);
-
   base::FilePath image_name =
       (test_case_ == GPU || test_case_ == SKIA_GL)
           ? base::FilePath(FILE_PATH_LITERAL("mask_of_backdrop_filter_gpu.png"))