godoc/static: prevent menu "bouncing" when showing Play button

The code as written would use JavaScript to show the "Play" button in
the menu when the Playground is enabled, making the button appear
after the page first renders, causing a visible "bounce" in the menu.
This change checks the condition (whether this is not the front page, or
"wide") in the template code, instead of with JavaScript after the page
has loaded.

Change-Id: Iccf0a344116372f3207158793be8c7734e67a4ae
Reviewed-on: https://go-review.googlesource.com/c/140798
Reviewed-by: Andrew Bonventre <andybons@golang.org>

godoc/static/godoc.html

@@ -57,7 +57,7 @@ window.trackEvent = function(category, action, opt_label, opt_value, opt_noninte
 {{if not .GoogleCN}}
 <a href="/blog/">Blog</a>
 {{end}}
-{{if .Playground}}
+{{if (and .Playground .Title)}}
 <a id="playgroundButton" href="http://play.golang.org/" title="Show Go Playground">Play</a>
 {{end}}
 <span class="search-box"><input type="search" id="search" name="q" placeholder="Search" aria-label="Search" required><button type="submit"><span><!-- magnifying glass: --><svg width="24" height="24" viewBox="0 0 24 24"><title>submit search</title><path d="M15.5 14h-.79l-.28-.27C15.41 12.59 16 11.11 16 9.5 16 5.91 13.09 3 9.5 3S3 5.91 3 9.5 5.91 16 9.5 16c1.61 0 3.09-.59 4.23-1.57l.27.28v.79l5 4.99L20.49 19l-4.99-5zm-6 0C7.01 14 5 11.99 5 9.5S7.01 5 9.5 5 14 7.01 14 9.5 11.99 14 9.5 14z"/><path d="M0 0h24v24H0z" fill="none"/></svg></span></button></span>

godoc/static/godocs.js

@@ -149,7 +149,6 @@ function setupDropdownPlayground() {
     button.removeClass('active');
     div.hide();
   });
-  button.show();
   $('#menu').css('min-width', '+=60');
 }
 

godoc/static/style.css

@@ -624,7 +624,6 @@ div.play .buttons a {
 }
 
 /* drop-down playground */
-#playgroundButton,
 div#playground {
 	/* start hidden; revealed by javascript */
 	display: none;