Temporarily disable a webgl conformance test on D3D9 only.

content/test/gpu/gpu_tests/webgl_conformance_expectations.py

Index: content/test/gpu/gpu_tests/webgl_conformance_expectations.py
diff --git a/content/test/gpu/gpu_tests/webgl_conformance_expectations.py b/content/test/gpu/gpu_tests/webgl_conformance_expectations.py
index 52c7790419cc2c174f2822a2cc09ed9f11de2201..2e782df9529805856ccf669bb145aa6f195cf79b 100644
--- a/content/test/gpu/gpu_tests/webgl_conformance_expectations.py
+++ b/content/test/gpu/gpu_tests/webgl_conformance_expectations.py
@@ -80,6 +80,8 @@ 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',