Suppress failling WebGL test on Linux Nvidia

WebglConformance_conformance2_context_methods_2 is failing sometimes on Linux Nvidia with
a GPU crash. Mark the test as flaky.

BUG=906212
TBR=kbr@chromium.org

Change-Id: I86bea7e01fde6b26b25d7fa27c8a9f41e5be9df7
Reviewed-on: https://chromium-review.googlesource.com/c/1340948Reviewed-by: Robert Kroeger <rjkroege@chromium.org>
Commit-Queue: Robert Kroeger <rjkroege@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609037}

content/test/gpu/gpu_tests/webgl_conformance_expectations.py

@@ -640,6 +640,8 @@ class WebGLConformanceExpectations(GpuTestExpectations):
     self.Flaky('conformance/textures/image/' +
                'tex-2d-rgb-rgb-unsigned_byte.html',
                ['linux', 'nvidia'], bug=596622)
+    self.Flaky('conformance2/context/methods-2.html',
+               ['linux', 'nvidia'], bug=906212)
 
     # NVIDIA P400 OpenGL
     self.Fail('conformance/limits/gl-max-texture-dimensions.html',