DevTools: prettify layout on Shortcuts help screen

BUG=394823

Review URL: https://codereview.chromium.org/400783002

git-svn-id: svn://svn.chromium.org/blink/trunk@178429 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/devtools/front_end/helpScreen.css

@@ -150,7 +150,9 @@ body.platform-mac .help-key-cell {
 }
 
 .help-cell {
-    display: inline;
+    display: inline-block;
+    width: 200px;
+    vertical-align: middle;
 }
 
 .help-section-title {