Bug 1455487 - Rotate the chevron icon 180 degree when RTL. r=jdescottes

If the browser ui direction is RTL, this patch will rotate the chevron menu
icon of devtool 180 degree.

MozReview-Commit-ID: 72vLKnF1FkF

--HG--
extra : rebase_source : f7905e66da57eaba5e03e850f6305a3d4ed534f5

devtools/client/themes/toolbox.css

@@ -160,6 +160,10 @@
   background-position: center;
 }
 
+.tools-chevron-menu:-moz-locale-dir(rtl) {
+  transform: rotate(180deg);
+}
+
 #toolbox-controls {
   margin-right: 3px;
 }