Fixing testBrowsingPostEntryWithButton flakiness.

ios/chrome/test/earl_grey/chrome_earl_grey.mm

Index: ios/chrome/test/earl_grey/chrome_earl_grey.mm
diff --git a/ios/chrome/test/earl_grey/chrome_earl_grey.mm b/ios/chrome/test/earl_grey/chrome_earl_grey.mm
index 8506bb71116a7130ff0b63318d6cb319233e3a7b..76020336692c3b1542159ff7dca47d51adbf8438 100644
--- a/ios/chrome/test/earl_grey/chrome_earl_grey.mm
+++ b/ios/chrome/test/earl_grey/chrome_earl_grey.mm
@@ -16,6 +16,7 @@
 #import "ios/chrome/test/app/history_test_util.h"
 #include "ios/chrome/test/app/navigation_test_util.h"
 #import "ios/chrome/test/app/static_html_view_test_util.h"
+#import "ios/chrome/test/earl_grey/chrome_matchers.h"
 #import "ios/testing/wait_util.h"
 #import "ios/web/public/test/earl_grey/js_test_util.h"
 #import "ios/web/public/test/web_view_interaction_test_util.h"
@@ -160,4 +161,21 @@ + (void)waitForStaticHTMLViewNotContainingText:(NSString*)text {
              @"Failed, there was a static html view containing %@", text);
 }
 
++ (void)waitForOmniboxText:(NSString*)text {
+  GREYCondition* condition = [GREYCondition
+      conditionWithName:@"Wait for omnibox text."
+                  block:^BOOL {
+                    NSError* error = nil;
+                    [[EarlGrey
+                        selectElementWithMatcher:chrome_test_util::OmniboxText(
+                                                     base::SysNSStringToUTF8(
+                                                         text))]

[gchatz, 2017/04/08 00:17:05]

Could the matcher be made a local variable to have better formatting?

[Eugene But (OOO till 7-30), 2017/04/08 00:20:36]

Using functions for matchers instead of local variables looks cleaner and it is
more reusable. In this case changing argument to std::string and adding |using
chrome_test_util::OmniboxText| would solve the formatting problem. But do we
even need |waitForOmniboxText:| API? Can we wait for web view text instead?

[liaoyuke, 2017/04/08 00:43:07]

replied in another comment, will make the change if we decide that
|waitForOmniboxText:| is needed.

+                        assertWithMatcher:grey_notNil()
+                                    error:&error];
+                    return error == nil;
+                  }];
+  GREYAssert([condition waitWithTimeout:testing::kWaitForUIElementTimeout],
+             @"Failed, omnibox was not %@", text);
+}
+
 @end