Mark WebGL2 canvas_sub_rectangle/tex-2d-rg16f-rg-float failing on Windows/OpenGL.

BUG=784849

TBR=zmo@chromium.org
NOTRY=true

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
Change-Id: Ic6316db156c1b68daf84ec804094a510ed6bab46
Reviewed-on: https://chromium-review.googlesource.com/769227
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#516356}

content/test/gpu/gpu_tests/webgl2_conformance_expectations.py

@@ -166,6 +166,9 @@ class WebGL2ConformanceExpectations(WebGLConformanceExpectations):
         ['win', 'nvidia', 'opengl'], bug=709874)
     self.Flaky('conformance2/rendering/attrib-type-match.html',
         ['win', 'nvidia', 'opengl'], bug=782254)
+    self.Fail('conformance2/textures/canvas_sub_rectangle/' +
+        'tex-2d-rg16f-rg-float.html',
+        ['win', 'nvidia', 'opengl'], bug=784849)
 
     # Win / AMD
     self.Fail('conformance2/rendering/blitframebuffer-stencil-only.html',