[Fuchsia] Add missing test filter for webgl_conformance tests.

Bug: 1080853
Change-Id: Ibdb7b1b295e2ee05016baea32358dbc6a18c4cba
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2523961
Auto-Submit: Chong Gu <chonggu@google.com>
Reviewed-by: Brian Sheedy <bsheedy@chromium.org>
Commit-Queue: Brian Sheedy <bsheedy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#825466}

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

@@ -165,6 +165,7 @@ crbug.com/1145951 [ fuchsia fuchsia-board-astro ] conformance/rendering/preserve
 # Specific build issue
 crbug.com/1146483 [ fuchsia fuchsia-board-astro ] conformance/textures/misc/tex-video-using-tex-unit-non-zero.html [ Skip ]
 crbug.com/1146483 [ fuchsia fuchsia-board-astro ] conformance/textures/misc/texture-upload-size.html [ Skip ]
+crbug.com/1146483 [ fuchsia fuchsia-board-astro ] conformance/textures/image_bitmap_from_video/tex-2d-alpha-alpha-unsigned_byte.html [ Skip ]
 crbug.com/1146483 [ fuchsia fuchsia-board-astro ] conformance/textures/video/tex-2d-alpha-alpha-unsigned_byte.html [ Skip ]
 
 # Flaky on Fuchsia hardware devices