Fix WebGL 2.0 expectations and skip a test with an assertion failure.

content/test/gpu/gpu_tests/webgl2_conformance_expectations.py

Index: content/test/gpu/gpu_tests/webgl2_conformance_expectations.py
diff --git a/content/test/gpu/gpu_tests/webgl2_conformance_expectations.py b/content/test/gpu/gpu_tests/webgl2_conformance_expectations.py
index 371afa2deb2ae9d874bd218a479515c7180bfae0..ae0ab0f8bdea60748db68dda94db033bb49e30d2 100644
--- a/content/test/gpu/gpu_tests/webgl2_conformance_expectations.py
+++ b/content/test/gpu/gpu_tests/webgl2_conformance_expectations.py
@@ -147,6 +147,12 @@ class WebGL2ConformanceExpectations(WebGLConformanceExpectations):
     self.Fail('conformance2/textures/video/tex-image-and-sub-image-2d' +
         '-with-video-rgb5_a1-rgba-unsigned_byte.html',
         ['win8'], bug=483282)
+    # Windows Debug. Causing assertions in the GPU process which raise
+    # a dialog box, so have to skip them rather than mark them as
+    # failing.
+    self.Skip('conformance2/textures/canvas/tex-image-and-sub-image-2d' +
+        '-with-canvas-rgba8-rgba-unsigned_byte.html',
+        ['win', 'debug'], bug=542901)
 
     # Mac only.
     self.Skip('deqp/data/gles3/shaders/qualification_order.html',