Mark oes-texture-half-float-with-video.html failing on Mac with NVIDIA GPU.

Unfortunately the flaky suppression isn't working in this situation.
Filed Issue 530373 about that.

BUG=524717
TBR=bajones@chromium.org,zmo@chromium.org

Review URL: https://codereview.chromium.org/1336793002

Cr-Commit-Position: refs/heads/master@{#348743}

content/test/gpu/gpu_tests/webgl_conformance_expectations.py

@@ -154,8 +154,8 @@ class WebGLConformanceExpectations(GpuTestExpectations):
     self.Fail(
         'conformance/glsl/bugs/array-of-struct-with-int-first-position.html',
         ['mac', ('nvidia', 0xfd5), ('nvidia', 0xfe9)], bug=368912)
-    self.Flaky('conformance/extensions/oes-texture-half-float-with-video.html',
-               ['mac', ('nvidia', 0xfd5), ('nvidia', 0xfe9)], bug=524717)
+    self.Fail('conformance/extensions/oes-texture-half-float-with-video.html',
+              ['mac', ('nvidia', 0xfd5), ('nvidia', 0xfe9)], bug=524717)
 
     # Mac / AMD Failures
     self.Fail('deqp/data/gles2/shaders/conversions.html',