Add a custom error message in EG WaitUtil

ios/testing/earl_grey/wait_util.h

Index: ios/testing/earl_grey/wait_util.h
diff --git a/ios/testing/earl_grey/wait_util.h b/ios/testing/earl_grey/wait_util.h
index 1a8db47ecde733890a2592e6184b57e286e46cc9..8ad5991d64aff877992dfd2f47f4b2f303a4d6f9 100644
--- a/ios/testing/earl_grey/wait_util.h
+++ b/ios/testing/earl_grey/wait_util.h
@@ -21,6 +21,12 @@ extern const NSTimeInterval kWaitForJSCompletionTimeout;
 // Waits until |condition| is true, or induces GREYAssert after |timeout|.
 void WaitUntilCondition(NSTimeInterval timeout, bool (^condition)(void));
 
+// Waits until |condition| is true, or induces GREYAssert after |timeout| with
+// |timeoutDescription| error message.
+void WaitUntilCondition(NSTimeInterval timeout,
+                        bool (^condition)(void),

[baxley, 2016/08/22 03:55:01]

nit: what do you think about moving the block parameter to be the last arg?
That's Apple's guidance, though I didn't see anything glancing at Google's
guide. Feel free to push back if you disagree, or find something elsewhere.

[gambard, 2016/08/22 07:11:04]

Done.

+                        NSString* timeoutDescription);
+
 }  // namespace testing
 
-#endif  // IOS_TESTING_EARL_GREY_WAIT_UTIL_H_
+#endif  // IOS_TESTING_EARL_GREY_WAIT_UTIL_H_