Add missing definition of swap in base::IntrusiveHeap

Change-Id: I508786031d2658ab907661caea71fa6e45270006
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1862686Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Jüri Valdmann <juri.valdmann@qt.io>
Cr-Commit-Position: refs/heads/master@{#707772}

base/containers/intrusive_heap.h

@@ -458,7 +458,7 @@ class IntrusiveHeap {
   // General operations.
 
   void swap(IntrusiveHeap& other) noexcept;
-  friend void swap(IntrusiveHeap& lhs, IntrusiveHeap& rhs);
+  friend void swap(IntrusiveHeap& lhs, IntrusiveHeap& rhs) { lhs.swap(rhs); }
 
   // Comparison operators. These check for exact equality. Two heaps that are
   // semantically equivalent (contain the same elements, but in different

base/containers/intrusive_heap_unittest.cc

@@ -585,6 +585,17 @@ TEST(IntrusiveHeapTest, Assignment) {
   ExpectCanonical(heap2);
 }
 
+TEST(IntrusiveHeapTest, Swap) {
+  IntrusiveHeapInt heap{CANONICAL_ELEMENTS};
+  IntrusiveHeapInt heap2;
+  swap(heap, heap2);
+  EXPECT_TRUE(heap.empty());
+  ExpectCanonical(heap2);
+  heap.swap(heap2);
+  EXPECT_TRUE(heap2.empty());
+  ExpectCanonical(heap);
+}
+
 TEST(IntrusiveHeapTest, ElementAccess) {
   IntrusiveHeapInt heap{CANONICAL_ELEMENTS};
   EXPECT_EQ(heap.front(), heap[0]);