Refactor wait_util so it isn't coupled to EarlGrey.

ios/web/shell/test/earl_grey/shell_matchers.mm

Index: ios/web/shell/test/earl_grey/shell_matchers.mm
diff --git a/ios/web/shell/test/earl_grey/shell_matchers.mm b/ios/web/shell/test/earl_grey/shell_matchers.mm
index 5e71d586fcaf04b655d23df432dffb640bcbae79..6b4e7875b810ae7f15c125fd1dfdf91d215f88e4 100644
--- a/ios/web/shell/test/earl_grey/shell_matchers.mm
+++ b/ios/web/shell/test/earl_grey/shell_matchers.mm
@@ -7,7 +7,7 @@
 #import "base/mac/foundation_util.h"
 #include "base/strings/sys_string_conversions.h"
 #import "ios/testing/earl_grey/matchers.h"
-#include "ios/testing/earl_grey/wait_util.h"
+#include "ios/testing/wait_util.h"
 #import "ios/web/public/web_state/web_state.h"
 #import "ios/web/public/test/earl_grey/web_view_matchers.h"
 #import "ios/web/shell/test/app/web_shell_test_util.h"
@@ -43,9 +43,17 @@ id<GREYMatcher> addressFieldText(std::string text) {
       return NO;
     }
     UITextField* text_field = base::mac::ObjCCastStrict<UITextField>(view);
-    testing::WaitUntilCondition(testing::kWaitForUIElementTimeout, ^bool() {
-      return [text_field.text isEqualToString:base::SysUTF8ToNSString(text)];
-    });
+    NSString* errorMessage = [NSString

[Eugene But (OOO till 7-30), 2016/10/25 14:43:39]

s/errorMessage/error_message

[baxley, 2016/10/25 18:50:05]

Done.

+        stringWithFormat:
+            @"Address field text did not match. expected: %@, actual: %@",
+            base::SysUTF8ToNSString(text), text_field.text];
+    GREYAssert(testing::WaitUntilConditionOrTimeout(
+                   testing::kWaitForUIElementTimeout,
+                   ^bool() {

[Eugene But (OOO till 7-30), 2016/10/25 14:43:39]

Optional nit (seems to be better formatting):

^{
  return text == base::SysNSStringToUTF8(text_field.text);
}

[baxley, 2016/10/25 18:50:05]

This is what git cl format did. Would you rather I create a variable, or add
using testing::kWaitFor... to see if that helps?

+                     return [text_field.text
+                         isEqualToString:base::SysUTF8ToNSString(text)];
+                   }),
+               errorMessage);
     return YES;
   };