[DevTools] Support broken UMA metric from M49 frontend.

This patch mitigates bad message crash due to wrong UMA metric
introduced in https://codereview.chromium.org/1520403004.
It was reverted later, but was not merged to M49.

BUG=603789

Review URL: https://codereview.chromium.org/1892743005

Cr-Commit-Position: refs/heads/master@{#387793}

front_end/devtools.js

@@ -525,6 +525,9 @@ InspectorFrontendHostImpl.prototype = {
      */
     recordEnumeratedHistogram: function(actionName, actionCode, bucketSize)
     {
+        // Support for M49 frontend.
+        if (actionName === "DevTools.DrawerShown")
+            return;
         DevToolsAPI.sendMessageToEmbedder("recordEnumeratedHistogram", [actionName, actionCode, bucketSize], null);
     },