Bug 1371962 - Rename the dir attribute added in bug 1357656 to labeldirection; r=mconley

This avoids using a reserved XUL attribute name.

browser/base/content/tabbrowser.css

@@ -51,14 +51,14 @@
   width: 0;
 }
 
-.tab-label-container[textoverflow][dir=ltr]:not([pinned]),
-.tab-label-container[textoverflow]:not([dir]):not([pinned]):-moz-locale-dir(ltr) {
+.tab-label-container[textoverflow][labeldirection=ltr]:not([pinned]),
+.tab-label-container[textoverflow]:not([labeldirection]):not([pinned]):-moz-locale-dir(ltr) {
   direction: ltr;
   mask-image: linear-gradient(to left, transparent, black 2em);
 }
 
-.tab-label-container[textoverflow][dir=rtl]:not([pinned]),
-.tab-label-container[textoverflow]:not([dir]):not([pinned]):-moz-locale-dir(rtl) {
+.tab-label-container[textoverflow][labeldirection=rtl]:not([pinned]),
+.tab-label-container[textoverflow]:not([labeldirection]):not([pinned]):-moz-locale-dir(rtl) {
   direction: rtl;
   mask-image: linear-gradient(to right, transparent, black 2em);
 }

browser/base/content/tabbrowser.xml

@@ -1549,7 +1549,7 @@
             let isRTL = dwu.getDirectionFromText(aLabel) == Ci.nsIDOMWindowUtils.DIRECTION_RTL;
 
             aTab.setAttribute("label", aLabel);
-            aTab.setAttribute("dir", isRTL ? "rtl" : "ltr");
+            aTab.setAttribute("labeldirection", isRTL ? "rtl" : "ltr");
             aTab._labelIsContentTitle = aOptions && aOptions.isContentTitle;
 
             // Dispatch TabAttrModified event unless we're setting the label
@@ -7271,7 +7271,7 @@
                      class="tab-icon-overlay"
                      role="presentation"/>
           <xul:hbox class="tab-label-container"
-                    xbl:inherits="pinned,selected=visuallyselected,dir"
+                    xbl:inherits="pinned,selected=visuallyselected,labeldirection"
                     onoverflow="this.setAttribute('textoverflow', 'true');"
                     onunderflow="this.removeAttribute('textoverflow');"
                     flex="1">