Revert of Temporarily disable a webgl conformance test on D3D9 only. (patchset...

Revert of Temporarily disable a webgl conformance test on D3D9 only. (patchset #1 id:1 of https://codereview.chromium.org/1135333004/)

Reason for revert:
Bug fixed.  Re-enabling the test.

Original issue's description:
> Temporarily disable a webgl conformance test on D3D9 only.
>
> BUG=488552
> TEST=webgl conformacne with D3D9 backend
> R=kbr@chromium.org
> NOTRY=true
>
> Committed: https://crrev.com/4fbdae9877d2b4775efa0dffdaa9c16ed6689c75
> Cr-Commit-Position: refs/heads/master@{#330138}

TBR=kbr@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=488552

Review URL: https://codereview.chromium.org/1124083006

Cr-Commit-Position: refs/heads/master@{#330652}

content/test/gpu/gpu_tests/webgl_conformance_expectations.py

@@ -80,8 +80,6 @@ class WebGLConformanceExpectations(GpuTestExpectations):
         ['win', 'd3d9'], bug=896) # angle bug ID
     self.Skip('conformance/extensions/oes-texture-half-float-with-canvas.html',
         ['win', 'd3d9'], bug=896) # angle bug ID
-    self.Fail('conformance/glsl/bugs/conditional-discard-optimization.html',
-        ['win', 'd3d9'], bug=488552)
 
     # Mac failures
     self.Fail('conformance/glsl/misc/shaders-with-invariance.html',