[heap-profiler] Make WeakMap => key value weak in heap snapshot.

Bug: chromium:875041
Change-Id: I4008fa2f7d92a0f2005c7566eb2945a800a9d284
Reviewed-on: https://chromium-review.googlesource.com/1190862
Commit-Queue: Alexei Filippov <alph@chromium.org>
Reviewed-by: Alexei Filippov <alph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55474}

src/profiler/heap-snapshot-generator.cc

@@ -1077,8 +1077,8 @@ void V8HeapExplorer::ExtractEphemeronHashTableReferences(
     Object* value = table->get(value_index);
     SetWeakReference(table, entry, key_index, key,
                      table->OffsetOfElementAt(key_index));
-    SetInternalReference(table, entry, value_index, value,
-                         table->OffsetOfElementAt(value_index));
+    SetWeakReference(table, entry, value_index, value,
+                     table->OffsetOfElementAt(value_index));
     HeapEntry* key_entry = GetEntry(key);
     int key_entry_index = key_entry->index();
     HeapEntry* value_entry = GetEntry(value);

test/cctest/test-heap-profiler.cc

@@ -686,7 +686,7 @@ TEST(HeapSnapshotWeakCollection) {
       ++weak_entries;
     }
   }
-  CHECK_EQ(1, weak_entries);  // Key is the only weak.
+  CHECK_EQ(2, weak_entries);  // Key and value are weak.
   const v8::HeapGraphNode* wm_s =
       GetProperty(env->GetIsolate(), wm, v8::HeapGraphEdge::kProperty, "str");
   CHECK(wm_s);