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..e99cce4a3d8f07f731407aed63eda0c3748f55e4 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,
+                        NSString* timeoutDescription,
+                        bool (^condition)(void));
+
 }  // namespace testing
 
-#endif  // IOS_TESTING_EARL_GREY_WAIT_UTIL_H_
+#endif  // IOS_TESTING_EARL_GREY_WAIT_UTIL_H_