Revert "Lift WebGL Mac test suppression."

This reverts commit 53e7fc6f.

Reason for revert: Immediately started flaking:

https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac%20FYI%20Release%20%28Intel%29/3698
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac%20FYI%20Release%20%28Intel%29/3707

Original change's description:
> Lift WebGL Mac test suppression.
> 
> Tentatively fixed.
> 
> Test: deqp/functional/gles3/shaderoperator/common_functions
> Bug: 820225
> 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: If66fee7d2beb1fecb9f9056425ee1dceb2a2acc1
> Tbr: kbr@chromium.org
> Reviewed-on: https://chromium-review.googlesource.com/1095333
> Reviewed-by: Jamie Madill <jmadill@chromium.org>
> Commit-Queue: Jamie Madill <jmadill@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#566110}

TBR=jmadill@chromium.org,kbr@chromium.org

Change-Id: Ia475bb6812aa31494339004bbfc85c663133d094
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 820225
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
Reviewed-on: https://chromium-review.googlesource.com/1097435Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Cr-Commit-Position: refs/heads/master@{#566431}

content/test/gpu/gpu_tests/webgl2_conformance_expectations.py

@@ -720,6 +720,8 @@ class WebGL2ConformanceExpectations(WebGLConformanceExpectations):
         ['mac', 'no_passthrough', 'intel'], bug=679692)
     self.Fail('deqp/functional/gles3/fbomultisample*',
         ['mac', 'intel'], bug=641209)
+    self.Fail('deqp/functional/gles3/shaderoperator/common_functions.html',
+        ['mac', 'intel'], bug=820225)
     self.Fail('deqp/functional/gles3/texturefiltering/2d_combinations_01.html',
         ['mac', 'intel'], bug=606074)
     self.Fail('deqp/functional/gles3/texturefiltering/' +