Add back on..Arrow functions. Add left/right key navigation in MessageEditor

src/components/views/elements/MessageEditor.js

@@ -116,6 +116,10 @@ export default class MessageEditor extends React.Component {
                     autoComplete.onUpArrow(event); break;
                 case "ArrowDown":
                     autoComplete.onDownArrow(event); break;
+                case "ArrowLeft":
+                    autoComplete.onLeftArrow(event); break;
+                case "ArrowRight":
+                    autoComplete.onRightArrow(event); break;
                 case "Tab":
                     autoComplete.onTab(event); break;
                 case "Escape":

src/editor/autocomplete.js

@@ -55,6 +55,22 @@ export default class AutocompleteWrapperModel {
         });
     }
 
+    onUpArrow() {
+        this._getAutocompleterComponent().moveSelection(-1);
+    }
+
+    onDownArrow() {
+        this._getAutocompleterComponent().moveSelection(+1);
+    }
+
+    onLeftArrow() {
+        this._getAutocompleterComponent().moveSelection(-1);
+    }
+
+    onRightArrow() {
+        this._getAutocompleterComponent().moveSelection(+1);
+    }
+
     onPartUpdate(part, offset) {
         // cache the typed value and caret here
         // so we can restore it in onComponentSelectionChange when the value is undefined (meaning it should be the typed text)