Suppress flaky WebGL failure on Win10 D3D9 passthrough

TBR=bajones@chromium.org

Bug: angleproject:4539
Change-Id: I7e05c18e09ac1e62ce631dfa66deef4aa3fe1f95
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2133978Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#756238}

content/test/gpu/gpu_tests/test_expectations/webgl_conformance_expectations.txt

@@ -200,6 +200,7 @@ crbug.com/680754 [ win10 nvidia-0x1cb3 d3d9 ] conformance/ogles/GL/cos/cos_001_t
 crbug.com/750896 [ win10 nvidia-0x1cb3 d3d9 ] conformance/textures/image_bitmap_from_video/* [ RetryOnFailure ]
 crbug.com/750896 [ win10 nvidia-0x1cb3 d3d9 ] conformance/textures/video/* [ RetryOnFailure ]
 crbug.com/829389 [ win10 nvidia-0x1cb3 d3d9 passthrough ] conformance/uniforms/uniform-samplers-test.html [ RetryOnFailure ]
+crbug.com/angleproject/4539 [ win10 nvidia-0x1cb3 d3d9 passthrough ] conformance/extensions/oes-texture-half-float-linear.html [ RetryOnFailure ]
 
 # Win10 / NVIDIA Quadro P400 failures
 crbug.com/728670 [ win10 nvidia-0x1cb3 ] conformance/textures/image_bitmap_from_video/tex-2d-rgba-rgba-unsigned_short_5_5_5_1.html [ RetryOnFailure ]