Suppress 2 flaky WebGL tests on Mac

conformance/ogles/GL/acos/acos_001_to_006.html
conformance/ogles/GL/asin/asin_001_to_006.html

Flaky DCHECK on multiple configs - Intel, AMD, Metal, OpenGL

TBR=bsheedy

Bug: 1108676
Change-Id: I0e81ad898cca9e0f862511c8d732ed89372858d5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2391589Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Reviewed-by: Brian Sheedy <bsheedy@chromium.org>
Commit-Queue: Yuly Novikov <ynovikov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804038}

content/test/gpu/gpu_tests/test_expectations/webgl_conformance_expectations.txt

@@ -419,6 +419,8 @@ crbug.com/1111652 [ win10 intel vulkan passthrough ] conformance/context/context
 crbug.com/844311 [ mac no-swiftshader-gl ] conformance/glsl/misc/fragcolor-fragdata-invariant.html [ Failure ]
 crbug.com/599272 [ mac no-passthrough ] conformance/extensions/oes-texture-float-with-video.html [ RetryOnFailure ]
 crbug.com/928926 [ mac ] conformance/ogles/GL/abs/abs_001_to_006.html [ RetryOnFailure ]
+crbug.com/1108676 [ mac ] conformance/ogles/GL/acos/acos_001_to_006.html [ RetryOnFailure ]
+crbug.com/1108676 [ mac ] conformance/ogles/GL/asin/asin_001_to_006.html [ RetryOnFailure ]
 
 # Mac AMD failures
 crbug.com/642822 [ mac amd ] conformance/rendering/clipping-wide-points.html [ Failure ]