Bug 404267 - Always allow click-through on scrollbars. r=roc

layout/generic/nsGfxScrollFrame.cpp

@@ -2198,6 +2198,8 @@ nsGfxScrollFrameInner::CreateAnonymousContent(nsTArray<nsIContent*>& aElements)
     NS_ENSURE_SUCCESS(rv, rv);
     mHScrollbarContent->SetAttr(kNameSpaceID_None, nsGkAtoms::orient,
                                 NS_LITERAL_STRING("horizontal"), PR_FALSE);
+    mHScrollbarContent->SetAttr(kNameSpaceID_None, nsGkAtoms::clickthrough,
+                                NS_LITERAL_STRING("always"), PR_FALSE);
     if (!aElements.AppendElement(mHScrollbarContent))
       return NS_ERROR_OUT_OF_MEMORY;
   }
@@ -2208,6 +2210,8 @@ nsGfxScrollFrameInner::CreateAnonymousContent(nsTArray<nsIContent*>& aElements)
     NS_ENSURE_SUCCESS(rv, rv);
     mVScrollbarContent->SetAttr(kNameSpaceID_None, nsGkAtoms::orient,
                                 NS_LITERAL_STRING("vertical"), PR_FALSE);
+    mVScrollbarContent->SetAttr(kNameSpaceID_None, nsGkAtoms::clickthrough,
+                                NS_LITERAL_STRING("always"), PR_FALSE);
     if (!aElements.AppendElement(mVScrollbarContent))
       return NS_ERROR_OUT_OF_MEMORY;
   }
@@ -2243,6 +2247,8 @@ nsGfxScrollFrameInner::CreateAnonymousContent(nsTArray<nsIContent*>& aElements)
     mScrollCornerContent->SetAttr(kNameSpaceID_None, nsGkAtoms::dir, dir, PR_FALSE);
     mScrollCornerContent->SetAttr(kNameSpaceID_None, nsGkAtoms::element,
                                   NS_LITERAL_STRING("_parent"), PR_FALSE);
+    mScrollCornerContent->SetAttr(kNameSpaceID_None, nsGkAtoms::clickthrough,
+                                  NS_LITERAL_STRING("always"), PR_FALSE);
 
     if (!aElements.AppendElement(mScrollCornerContent))
       return NS_ERROR_OUT_OF_MEMORY;

toolkit/content/widgets/scrollbar.xml

@@ -17,7 +17,7 @@
   </binding>
 
   <binding id="scrollbar" extends="chrome://global/content/bindings/scrollbar.xml#scrollbar-base">
-    <content>
+    <content allowclickthrough="always">
       <xul:scrollbarbutton sbattr="scrollbar-up-top" type="decrement" xbl:inherits="curpos,maxpos,disabled,sborient=orient"/>
       <xul:scrollbarbutton sbattr="scrollbar-down-top" type="increment" xbl:inherits="curpos,maxpos,disabled,sborient=orient"/>
       <xul:slider flex="1" xbl:inherits="disabled,curpos,maxpos,pageincrement,increment,orient,sborient=orient">