[heap] Introduce enum of garbage collection reasons.

src/debug/debug.cc

Index: src/debug/debug.cc
diff --git a/src/debug/debug.cc b/src/debug/debug.cc
index bf6203f46e54d03a8f16d74d60e5c1627ead1e6c..747093e7492cb2119ee3d8008ef9492f713d56cf 100644
--- a/src/debug/debug.cc
+++ b/src/debug/debug.cc
@@ -1282,7 +1282,7 @@ bool Debug::PrepareFunctionForBreakPoints(Handle<SharedFunctionInfo> shared) {
 
   // Make sure we abort incremental marking.
   isolate_->heap()->CollectAllGarbage(Heap::kMakeHeapIterableMask,
-                                      "prepare for break points");
+                                      GarbageCollectionReason::kDebugger);
 
   DCHECK(shared->is_compiled());
   bool baseline_exists = shared->HasBaselineCode();
@@ -1599,7 +1599,8 @@ void Debug::ClearMirrorCache() {
 
 
 Handle<FixedArray> Debug::GetLoadedScripts() {
-  isolate_->heap()->CollectAllGarbage();
+  isolate_->heap()->CollectAllGarbage(Heap::kFinalizeIncrementalMarkingMask,
+                                      GarbageCollectionReason::kDebugger);
   Factory* factory = isolate_->factory();
   if (!factory->script_list()->IsWeakFixedArray()) {
     return factory->empty_fixed_array();