Show all mailto: handlers, but dim unavailable ones.

ios/chrome/browser/web/fake_mailto_handler_helpers.mm

Index: ios/chrome/browser/web/fake_mailto_handler_helpers.mm
diff --git a/ios/chrome/browser/web/fake_mailto_handler_helpers.mm b/ios/chrome/browser/web/fake_mailto_handler_helpers.mm
index 870298e552436d72f4acaf0091980d988969eddf..c87eee89464dc948a2a04a4e72047bf2a702ce7c 100644
--- a/ios/chrome/browser/web/fake_mailto_handler_helpers.mm
+++ b/ios/chrome/browser/web/fake_mailto_handler_helpers.mm
@@ -20,6 +20,18 @@
 }
 @end
 
+@implementation FakeMailtoHandlerForTesting
+- (instancetype)init {
+  return [super initWithName:@"FakeMail" appStoreID:@"12345678"];
+}
+- (BOOL)isAvailable {
+  return NO;
+}
+- (NSString*)beginningScheme {
+  return @"fakemail:/compose?";
+}
+@end
+
 @implementation CountingMailtoURLRewriterObserver
 @synthesize changeCount = _changeCount;
 - (void)rewriterDidChange:(MailtoURLRewriter*)rewriter {