Bug 856127 - Override the override. r=bz
Bug 853709 - Deny accessor definitions in SecurityWrapper. r=mrbkap
Bug 789897 - Implement isExtensible and preventExtensions traps for proxies, including scriptable direct proxies, and in the various wrapper classes.  Also move non-static JSObject::preventExtensions to static ObjectImpl::preventExtensions, for handle correctness.  Patch is a semi-tag-team effort with jwalden.  r=jwalden, r=ejpbruel, r=bholley, r=two-turtle-doves-and-a-partridge-in-a-pear-tree

--HG--
extra : rebase_source : 156d2c22499372fceb60d130e363a3685e68b9fc
Bug 853946: Replace flex container's cached content-box cross-size and cached ascent with local variables in Reflow(). rs=Waldo
Bug 785468: Compute flex container's baseline as-described in the spec. r=dbaron
Bug 841876: Enable flexbox pref in release builds. r=dbaron
Bug 856199: Remove nsHTMLReflowState's no-longer-needed AutoRestore #include. r=dbaron