cppgc: Fix GC flags for CppHeap.

The new flags enum had kReduceMemory as the first value, which means it
got the value 0 and thus was considered as never set.

Bug: v8:12407, chromium:1274954
Change-Id: Ifcce2316c1dcd09a12ad52ef391f513b014aea1c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3310609Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78189}

src/heap/cppgc-js/cpp-heap.h

@@ -31,9 +31,10 @@ class V8_EXPORT_PRIVATE CppHeap final
       public v8::CppHeap,
       public cppgc::internal::StatsCollector::AllocationObserver {
  public:
-  enum GarbageCollectionFlagValues {
-    kReduceMemory,
-    kForced,
+  enum GarbageCollectionFlagValues : uint8_t {
+    kNoFlags = 0,
+    kReduceMemory = 1 << 1,
+    kForced = 1 << 2,
   };
 
   using GarbageCollectionFlags = base::Flags<GarbageCollectionFlagValues>;
@@ -165,6 +166,8 @@ class V8_EXPORT_PRIVATE CppHeap final
   friend class MetricRecorderAdapter;
 };
 
+DEFINE_OPERATORS_FOR_FLAGS(CppHeap::GarbageCollectionFlags)
+
 }  // namespace internal
 }  // namespace v8