Suppress ContextLost.WebGLContextLostFromSelectElement flakes on OS X 10.7.

BUG=498149

Review URL: https://codereview.chromium.org/1176723002

Cr-Commit-Position: refs/heads/master@{#333661}

content/test/gpu/gpu_tests/context_lost_expectations.py

@@ -19,3 +19,7 @@ class ContextLostExpectations(GpuTestExpectations):
     # Mac 10.8 (ideally should restrict this to Debug, too)
     self.Fail('ContextLost.WebGLContextLostFromSelectElement',
               ['mountainlion'], bug=497411)
+
+    # Flaky on Mac 10.7 (ideally should restrict this to Debug, too)
+    self.Fail('ContextLost.WebGLContextLostFromSelectElement',
+              ['lion'], bug=498149)