Add test support for setting selected text option for <select> multiple

The test framework returns an empty string as the localized strings are
not supported. This caused the assert to fail on android debug builds,
because of which https://codereview.chromium.org/541693003/ had to be
reverted. This is the chromium side changes needed for the patch to be
restored.

BUG=401506

Review URL: https://codereview.chromium.org/593113003

Cr-Commit-Position: refs/heads/master@{#296648}

content/test/test_webkit_platform_support.cc

@@ -200,6 +200,8 @@ blink::WebString TestWebKitPlatformSupport::queryLocalizedString(
     return base::ASCIIToUTF16("range underflow");
   if (name == blink::WebLocalizedString::ValidationRangeOverflow)
     return base::ASCIIToUTF16("range overflow");
+  if (name == blink::WebLocalizedString::SelectMenuListText)
+    return base::ASCIIToUTF16("$1 selected");
   return BlinkPlatformImpl::queryLocalizedString(name, value);
 }