Update WebGL2 conformance test expectations to get Linux/AMD green

BUG=913301
TEST=Linux/AMD bot
TBR=jdarpinion@chromium.org
NOTRY=true

Change-Id: I8eab8e0326d4bb01043047ecfe4064453603daae
Reviewed-on: https://chromium-review.googlesource.com/c/1387694
Commit-Queue: Zhenyao Mo <zmo@chromium.org>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#618412}

content/test/gpu/gpu_tests/webgl2_conformance_expectations.py

@@ -1293,6 +1293,10 @@ class WebGL2ConformanceExpectations(WebGLConformanceExpectations):
     self.Fail('conformance2/buffers/get-buffer-sub-data-validity.html',
         ['linux', ('amd', 0x6613)], bug=851159)
 
+    self.Fail('conformance2/textures/misc/' +
+        'generate-mipmap-with-large-base-level.html',
+        ['linux', ('amd', 0x6613)], bug=913301)
+
     ####################
     # Android failures #
     ####################