Bug 1401638 - Fixup implicit constructor bustage. r=me on a CLOSED TREE

gfx/2d/DrawTargetCapture.h

@@ -170,7 +170,7 @@ private:
 
   struct PushedLayer
   {
-    PushedLayer(bool aOldPermitSubpixelAA)
+    explicit PushedLayer(bool aOldPermitSubpixelAA)
       : mOldPermitSubpixelAA(aOldPermitSubpixelAA)
     {}
     bool mOldPermitSubpixelAA;