extensions: fix dev controls spacing issue.

chrome/browser/resources/extensions/extensions.css

Index: chrome/browser/resources/extensions/extensions.css
diff --git a/chrome/browser/resources/extensions/extensions.css b/chrome/browser/resources/extensions/extensions.css
index 02241100aeddf8747e1ee28c01103b1d7abc217d..be9384e284f0502d5af7db6568e2d6a0deb5982e 100644
--- a/chrome/browser/resources/extensions/extensions.css
+++ b/chrome/browser/resources/extensions/extensions.css
@@ -49,6 +49,10 @@ html:not(.focus-outline-visible)
   white-space: nowrap;
 }
 
+#dev-controls button:not(:last-of-type) {
+  -webkit-margin-end: 5px;

[not at google - send to devlin, 2015/02/04 20:39:01]

I see that other WebUI buttons look fine, and don't need special treatment (or
at least they already seem to have it). Why is this code needed?

+}
+
 #apps-developer-tools-promo {
   align-items: center;
   border-top: 1px solid #eee;