Fix broken new line on gr-textarea in firefox

The --iron-autogrow-textarea_-_white-space is normal by default,
which will be interpreted differently between chrome and firefox.

Bug: Issue 11470
Change-Id: I15b37b5732ff0f2f5e28280a160c4ca26430a2e3
diff --git a/polygerrit-ui/app/elements/shared/gr-textarea/gr-textarea.html b/polygerrit-ui/app/elements/shared/gr-textarea/gr-textarea.html
index 131dc79..fa54dba 100644
--- a/polygerrit-ui/app/elements/shared/gr-textarea/gr-textarea.html
+++ b/polygerrit-ui/app/elements/shared/gr-textarea/gr-textarea.html
@@ -55,6 +55,9 @@
       iron-autogrow-textarea {
         padding: 2px;
         position: relative;
+
+        /** This is needed for firefox */
+        --iron-autogrow-textarea_-_white-space: pre-wrap;
       }
       #textarea.noBorder {
         border: none;