Update WebGL CTS expectations

conformance/glsl/misc/shaders-with-invariance.html should pass
with passthrough command buffer
since https://chromium-review.googlesource.com/446870 landed.

BUG=angleproject:1876
TBR=kbr@chromium.org
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2737663002
Cr-Commit-Position: refs/heads/master@{#455104}

content/test/gpu/gpu_tests/webgl_conformance_expectations.py

@@ -128,8 +128,6 @@ def SetExpectations(self):
         'resize.html', ['passthrough'], bug=665521)
     self.Fail('conformance/glsl/misc/shader-with-dfdx.frag.html',
         ['passthrough'], bug=1639) # angle bug ID
-    self.Fail('conformance/glsl/misc/shaders-with-invariance.html',
-        ['passthrough'], bug=1639) # angle bug ID
     self.Fail('conformance/glsl/misc/shaders-with-name-conflicts.html',
         ['passthrough'], bug=1639) # angle bug ID
     self.Fail('conformance/misc/invalid-passed-params.html',