Disable flaky GpuCrash.GPUProcessCrashesExactlyOnce test on mac and linux.

content/test/gpu/gpu_tests/context_lost_expectations.py

Index: content/test/gpu/gpu_tests/context_lost_expectations.py
diff --git a/content/test/gpu/gpu_tests/context_lost_expectations.py b/content/test/gpu/gpu_tests/context_lost_expectations.py
index cf80d118c1453d96a6a00bab1f5169c0eb7be179..52505c91bc149599dbc3cd9964c372d24ea23e3e 100644
--- a/content/test/gpu/gpu_tests/context_lost_expectations.py
+++ b/content/test/gpu/gpu_tests/context_lost_expectations.py
@@ -30,3 +30,10 @@ class ContextLostExpectations(GpuTestExpectations):
               ['mountainlion', 'debug'], bug=497411)
     self.Skip('ContextLost.WebGLContextLostFromSelectElement',
               ['lion', 'debug'], bug=498149)
+
+    # Flaky on linux_chromium_rel_ng and mac_chromium_rel_ng bots.
+    self.Flaky('GpuCrash.GPUProcessCrashesExactlyOnce',
+               ['linux'], bug=608923)
+    self.Flaky('GpuCrash.GPUProcessCrashesExactlyOnce',
+               ['mac'], bug=608923)
+