Mark WebGL test gl-bindAttribLocation-matrix.html flaky

TBR=kbr@chromium.org
BUG=906092

Change-Id: I11105b926d35b5bcb16c2930c04f98db20e5f4b4
Reviewed-on: https://chromium-review.googlesource.com/c/1340788Reviewed-by: Ella Ge <eirage@chromium.org>
Commit-Queue: Ella Ge <eirage@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608946}

content/test/gpu/gpu_tests/webgl_conformance_expectations.py

@@ -820,6 +820,8 @@ class WebGLConformanceExpectations(GpuTestExpectations):
         bug=610951)
     self.Fail('WebglExtension_EXT_sRGB',
         ['android', ('qualcomm', 'Adreno (TM) 418')], bug=610951)
+    self.Flaky('conformance/attribs/gl-bindAttribLocation-matrix.html',
+        ['android', ('qualcomm', 'Adreno (TM) 418')], bug=906092)
 
     # Nexus 6 (Adreno 420) and 6P (Adreno 430)
     self.Fail('conformance/context/' +