import changes from `dev' branch of rmottola/Arctic-Fox:

- Bug 1194028 - Part 1: Implement Animation NotifyEffectTimingUpdate and KeyframeEffect SetTiming. r=bbirtles (ebdf90981)
- Bug 1194028 - Part 2: Use KeyFrameEffect SetTiming. r=bbirtles (770edf4ab)
- Bug 1187804 - Annotate fixed-position layers with the scroll id of the scroll frame that they are fixed with respect to. r=mattwoodrow (b37b8a9e6)
- Bug 1209471 - Fix group used for Array.concat result, r=jandem. (fa0aba56d)
- missing tests of Bug 1183623, redirect keyup events to keydown target when focus shifts from chrome to content in-between (15634dd01)
- Bug 1183623, redirect keyup events to keydown target when focus shifts from chrome to content in-between, r=smaug (7316efd4f)
- pointer style (daaa76131)
- Bug 1155238: use RelengAPI-based Tooltool server. r=coop (9501de0ac)
- Bug 1140182: JS GDB pretty-printers: Implement pretty-printer for js::AbstractFramePtr. r=sfink (02228c34e)
- Bug 1139535: In js/src/gdb: Remove workaround for 2012 GDB bug. DONTBUILD r=sfink (7e08a0070)
- Bug 1140179: Adapt to new JSObject structure, which indirects through the ObjectGroup. DONTBUILD r=sfink (9c93cf5f8)
- Bug 1141032: fix = instead of == in an assert in NativeRegexpMacroAssembler.cpp; r=h4writer (f07efb736)
- Bug 1137573 - OdinMonkey: Generalize alignment analysis to handle adds with multiple uses r=luke a=ryanvm (0c437d56c)
- spacing (6938ecef8)
- Bug 1151326 - Don't inline yields in legacy generators in Baseline. r=shu (89b09ea28)
- pointer style (12437a045)
- Bug 1151634 - Patch a valid return address for debug mode OSR from exception handler when profiling is enabled. (r=jandem) (0453d85b7)
- pointer style (3e4a597ca)
- Pointer style (d0e273439)
- pointer style (ec0540b7c)

js/src/jsarray.cpp

@@ -2705,7 +2705,7 @@ js::array_concat(JSContext* cx, unsigned argc, Value* vp)
             }
         }
     } else {
-        narr = NewDenseEmptyArray(cx);
+        narr = NewFullyAllocatedArrayTryReuseGroup(cx, aobj, 0);
         if (!narr)
             return false;
         args.rval().setObject(*narr);