Fix DOMObserver mutation data for IE (facebookarchive#2285)

Summary:
Pull Request resolved: facebookarchive#2285

IE 11 considers the enter keypress that concludes the composition as an input char, which ends up adding a new line to the editor. I am adding code to strip that newline character when processing the mutation event.

Reviewed By: mrkev

Differential Revision: D19141003

fbshipit-source-id: 53848e42d0e2b45d609e6623cc5d5579168b73fe

src/component/handlers/composition/DOMObserver.js

@@ -110,6 +110,12 @@ class DOMObserver {
       // These events are also followed by a `childList`, which is the one
       // we are able to retrieve the offsetKey and apply the '' text.
       if (target.textContent !== '') {
+        // IE 11 considers the enter keypress that concludes the composition
+        // as an input char. This strips that newline character so the draft
+        // state does not receive spurious newlines.
+        if (USE_CHAR_DATA) {
+          return target.textContent.replace('\n', '');
+        }
         return target.textContent;
       }
     } else if (type === 'childList') {