Bug 1646321 - Do a GC_SHRINK on large-alloc failure. r=jonco

If a large allocation fails, do what we can to free up memory,
including discarding code if necessary - sometimes the failing
allocation is looking for code memory.

Differential Revision: https://phabricator.services.mozilla.com/D79990

js/src/shell/js.cpp

@@ -1935,7 +1935,7 @@ static void my_LargeAllocFailCallback() {
   MOZ_ASSERT(!JS::RuntimeHeapIsBusy());
 
   JS::PrepareForFullGC(cx);
-  cx->runtime()->gc.gc(GC_NORMAL, JS::GCReason::SHARED_MEMORY_LIMIT);
+  cx->runtime()->gc.gc(GC_SHRINK, JS::GCReason::SHARED_MEMORY_LIMIT);
 }
 
 static const uint32_t CacheEntry_SOURCE = 0;