Create EarlGrey wait utility.

ios/testing/earl_grey/wait_util.mm

Index: ios/testing/earl_grey/wait_util.mm
diff --git a/ios/testing/earl_grey/wait_util.mm b/ios/testing/earl_grey/wait_util.mm
index 798ce1cb2ad812e760b54665184021122269268e..962a20a2a00b02647307e8bce3e75cc50d64bb5e 100644
--- a/ios/testing/earl_grey/wait_util.mm
+++ b/ios/testing/earl_grey/wait_util.mm
@@ -4,9 +4,24 @@
 
 #include "ios/testing/earl_grey/wait_util.h"
 
+#import <EarlGrey/EarlGrey.h>
+
+#include "base/test/ios/wait_util.h"
+
 namespace testing {
 
 const NSTimeInterval kSpinDelaySeconds = 0.01;
-const NSTimeInterval kWaitForUIElementTimeout = 4.0;
 const NSTimeInterval kWaitForJSCompletionTimeout = 2.0;
+const NSTimeInterval kWaitForUIElementTimeout = 4.0;
+
+void WaitUntilCondition(NSTimeInterval timeout, bool (^condition)(void)) {
+  NSDate* deadline = [NSDate dateWithTimeIntervalSinceNow:timeout];
+  while (!condition() &&
+         [[NSDate date] compare:deadline] != NSOrderedDescending) {
+    base::test::ios::SpinRunLoopWithMaxDelay(
+        base::TimeDelta::FromSecondsD(testing::kSpinDelaySeconds));
+  }
+  GREYAssert(condition(), @"Timeout waiting for condition.");
 }
+
+}  // namespace testing