Bug 1609402 - Improve flakey test that relied on being able to alloca…

…te 1MB of GC things in under 5 seconds r=sfink

Tests that involve timing are often problematic.  Here we're checking that hitting the heap limit inside the five second time limit we set for skipping last ditch GCs doesn't trigger a GC, but allocating enough to hit this limit can take longer than five seconds on a busy system.

The patch makes the max heap size much smaller and so reduces the possibility that that this can happen.

Differential Revision: https://phabricator.services.mozilla.com/D60655

UltraBlame original commit: 86c17304b4ad481b4e2ad4def4b44b4f759ef563

js/src/jit-test/tests/gc/bug-1505622.js

@@ -131,12 +131,28 @@ small
 heap
 limit
 .
+gc
+(
+)
+;
+let
+currentSize
+=
+gcparam
+(
+"
+gcBytes
+"
+)
+;
 gcparam
 (
 "
 maxBytes
 "
-1024
+currentSize
++
+16
 *
 1024
 )