Bug 1657205 - Fallibly allocate for StartupCache from Omnijar r=froydnj

This changes the StartupCache::PutBuffer call from Omnijar to use a
fallibly allocated buffer, to reduce OOM crashes. We can/should broaden the
scope of this, but this is a simple initial change to mitigate the OOM
crashed introduced with bug 1627075.

Differential Revision: https://phabricator.services.mozilla.com/D86067

xpcom/build/Omnijar.cpp

@@ -14,6 +14,7 @@
 #include "nsNetUtil.h"
 #include "mozilla/scache/StartupCache.h"
 #include "mozilla/MmapFaultHandler.h"
+#include "mozilla/UniquePtrExtensions.h"
 
 namespace mozilla {
 
@@ -438,12 +439,14 @@ void CacheAwareZipReader::PutBufferIntoCache(const nsCString& aCacheKey,
   }
 
   auto* cache = scache::StartupCache::GetSingleton();
-  auto dataCopy = MakeUnique<char[]>(aSize);
+  auto dataCopy = MakeUniqueFallible<char[]>(aSize);
 
-  MMAP_FAULT_HANDLER_BEGIN_BUFFER(aBuffer, aSize)
-  memcpy(dataCopy.get(), aBuffer, aSize);
-  MMAP_FAULT_HANDLER_CATCH()
-  Unused << cache->PutBuffer(aCacheKey.get(), std::move(dataCopy), aSize);
+  if (dataCopy) {
+    MMAP_FAULT_HANDLER_BEGIN_BUFFER(aBuffer, aSize)
+    memcpy(dataCopy.get(), aBuffer, aSize);
+    MMAP_FAULT_HANDLER_CATCH()
+    Unused << cache->PutBuffer(aCacheKey.get(), std::move(dataCopy), aSize);
+  }
 }
 
 void CacheAwareZipReader::PushSuspendStartupCacheWrites() {