Create ChromeEarlGrey waitForWebViewContainingText.

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

Index: ios/web/shell/test/earl_grey/shell_earl_grey.mm
diff --git a/ios/web/shell/test/earl_grey/shell_earl_grey.mm b/ios/web/shell/test/earl_grey/shell_earl_grey.mm
index bdf8f1b47face21f3577251265b48677eb79864c..ed21c5b2f2465049e99602973be516d28d5d23d8 100644
--- a/ios/web/shell/test/earl_grey/shell_earl_grey.mm
+++ b/ios/web/shell/test/earl_grey/shell_earl_grey.mm
@@ -8,6 +8,7 @@
 
 #import "ios/testing/wait_util.h"
 #import "ios/web/public/test/earl_grey/js_test_util.h"
+#import "ios/web/public/test/web_view_content_test_util.h"
 #include "ios/web/shell/test/app/navigation_test_util.h"
 #import "ios/web/shell/test/app/web_shell_test_util.h"
 
@@ -40,4 +41,15 @@
   [[GREYUIThreadExecutor sharedInstance] drainUntilIdle];
 }
 
++ (void)waitForWebViewContainingText:(std::string)text {
+  GREYCondition* condition = [GREYCondition
+      conditionWithName:@"Wait for web view containing text"
+                  block:^BOOL {
+                    return web::test::IsWebViewContainingText(
+                        web::shell_test_util::GetCurrentWebState(), text);
+                  }];
+  GREYAssert([condition waitWithTimeout:testing::kWaitForUIElementTimeout],
+             @"Failed waiting for web view containing %s", text.c_str());
+}
+
 @end