Mark deqp/functional/gles3/shaderindexing/mat_01.html flaky on Mac Pro AMD.

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 c34c268f5e1fc6e032aaf641097cba2d0e537acd..90775831fc41100f7304df0d08c8637f11e1d1b7 100644
--- a/content/test/gpu/gpu_tests/webgl2_conformance_expectations.py
+++ b/content/test/gpu/gpu_tests/webgl2_conformance_expectations.py
@@ -397,6 +397,10 @@ class WebGL2ConformanceExpectations(WebGLConformanceExpectations):
     self.Fail('deqp/functional/gles3/shaderoperator/geometric.html',
         ['mac', 'amd'], bug=483282)
 
+    # Mac Pro with AMD GPU
+    self.Flaky('deqp/functional/gles3/shaderindexing/mat_01.html',
+        ['mac', ('amd', 0x679e)], bug=636648)
+
     # Mac Intel
     self.Fail('deqp/functional/gles3/shadercommonfunction.html',
         ['mac', 'intel'], bug=483282)