Trigger GC when crossing warning threshold on iOS

https://bugs.webkit.org/show_bug.cgi?id=273830
rdar://127677553

Reviewed by Geoffrey Garen.

On iOS where we have fairly strict memory limits, sometimes the mutator can get far ahead of the
GC. We might wait until a PROC_LIMIT_CRITICAL event fires before a full GC occurs, at which point
the process is already eligible to be killed by the OS.

To try and reduce the number of foreground OOMs, let's also trigger a full GC if it hasn't occurred
recently when a PROC_LIMIT_WARNING event fires (which is 80% of the critical threshold).

* Source/WebCore/page/MemoryRelease.cpp:
(WebCore::releaseMemory):

Canonical link: https://commits.webkit.org/278567@main

Source/WebCore/page/MemoryRelease.cpp

@@ -160,6 +160,11 @@ void releaseMemory(Critical critical, Synchronous synchronous, MaintainBackForwa
 {
     TraceScope scope(MemoryPressureHandlerStart, MemoryPressureHandlerEnd, static_cast<uint64_t>(critical), static_cast<uint64_t>(synchronous));
 
+#if PLATFORM(IOS_FAMILY)
+    if (critical == Critical::No)
+        GCController::singleton().garbageCollectNowIfNotDoneRecently();
+#endif
+
     if (critical == Critical::Yes) {
         // Return unused pages back to the OS now as this will likely give us a little memory to work with.
         WTF::releaseFastMallocFreeMemory();