Bug 1527532 - Make initial nursery size smaller r=sfink

Differential Revision: https://phabricator.services.mozilla.com/D19349

--HG--
extra : moz-landing-system : lando

js/src/gc/Nursery.cpp

@@ -142,7 +142,7 @@ bool js::Nursery::init(uint32_t maxNurseryBytes, AutoLockGCBgAlloc& lock) {
   if (!allocateNextChunk(0, lock)) {
     return false;
   }
-  capacity_ = NurseryChunkUsableSize;
+  capacity_ = SubChunkLimit;
   /* After this point the Nursery has been enabled */
 
   setCurrentChunk(0, true);