Bug 1451576 - Set dir=auto on [Browse...] button of <input type=file> r=Ehsan

The label of the button comes from the UI; it's direction should be independent
of the web content directionality. As there is no access to :-moz-locale-dir()
selectors in HTML, we'll have to rely on auto-direction here.

The alternative (or, addition to the fix here) would be adding the value of
the dir attribute to HtmlForm.properties, allowing the localizers to set
the directionality explicitly. I however don't know if that's necessary.

MozReview-Commit-ID: 5NXeLtxLXVH

layout/forms/nsFileControlFrame.cpp

@@ -87,6 +87,8 @@ MakeAnonButton(nsIDocument* aDoc, const char* labelKey,
   button->SetIsNativeAnonymousRoot();
   button->SetAttr(kNameSpaceID_None, nsGkAtoms::type,
                   NS_LITERAL_STRING("button"), false);
+  button->SetAttr(kNameSpaceID_None, nsGkAtoms::dir,
+                  NS_LITERAL_STRING("auto"), false);
 
   // Set the file picking button text depending on the current locale.
   nsAutoString buttonTxt;