Create temporary Earl Grey test that is flaky on FYI.

ios/web/shell/test/web_shell_navigation_egtest.mm

Index: ios/web/shell/test/web_shell_navigation_egtest.mm
diff --git a/ios/web/shell/test/web_shell_navigation_egtest.mm b/ios/web/shell/test/web_shell_navigation_egtest.mm
index e3a58281a5b9764af9cfc3d648af87073c3298d2..26fad4390cdf49ab6b56446d157b26ee165b0144 100644
--- a/ios/web/shell/test/web_shell_navigation_egtest.mm
+++ b/ios/web/shell/test/web_shell_navigation_egtest.mm
@@ -139,4 +139,11 @@
       assertWithMatcher:grey_notNil()];
 }
 
+// Tests that sometimes passing and failing makes the bots red.
+// TODO(crbug.com/614729): Remove this test once it is verified that
+// infrastructure is properly working.
+- (void)testCoinFlip {
+  GREYAssertTrue(arc4random_uniform(10) < 5, @"Failed coin flip.");

[baxley, 2016/05/25 16:36:56]

I used arc4random since it's included in stdlib, and we don't need to add any
imports for base that could be at risk of not being removed (i.e. all the code
added is contained in this method).

+}
+
 @end