Change the return type of WTF::bind() to |OwnPtr<Function>|

Source/platform/heap/HeapTest.cpp

Index: Source/platform/heap/HeapTest.cpp
diff --git a/Source/platform/heap/HeapTest.cpp b/Source/platform/heap/HeapTest.cpp
index 4edef2f13541959f0f45a07da23c681843b3887c..b0cc938c0a1af8471e22baafffd763ddeb8635b0 100644
--- a/Source/platform/heap/HeapTest.cpp
+++ b/Source/platform/heap/HeapTest.cpp
@@ -4302,21 +4302,21 @@ TEST(HeapTest, RegressNullIsStrongified)
 
 TEST(HeapTest, Bind)
 {
-    Closure closure = bind(&Bar::trace, Bar::create(), static_cast<Visitor*>(0));
+    OwnPtr<Closure> closure = bind(&Bar::trace, Bar::create(), static_cast<Visitor*>(0));
     Heap::collectGarbage(ThreadState::NoHeapPointersOnStack);
     // The closure should have a persistent handle to the Bar.
     EXPECT_EQ(1u, Bar::s_live);
 
-    Closure closure2 = bind(&Bar::trace, RawPtr<Bar>(Bar::create()), static_cast<Visitor*>(0));
+    OwnPtr<Closure> closure2 = bind(&Bar::trace, RawPtr<Bar>(Bar::create()), static_cast<Visitor*>(0));
     Heap::collectGarbage(ThreadState::NoHeapPointersOnStack);
     // The closure should have a persistent handle to the Bar.
     EXPECT_EQ(2u, Bar::s_live);
     // RawPtr<OffHeapInt> should not make Persistent.
-    Closure closure3 = bind(&OffHeapInt::voidFunction, RawPtr<OffHeapInt>(OffHeapInt::create(1).get()));
+    OwnPtr<Closure> closure3 = bind(&OffHeapInt::voidFunction, RawPtr<OffHeapInt>(OffHeapInt::create(1).get()));
 
     UseMixin::s_traceCount = 0;
     Mixin* mixin = UseMixin::create();
-    Closure mixinClosure = bind(&Mixin::trace, mixin, static_cast<Visitor*>(0));
+    OwnPtr<Closure> mixinClosure = bind(&Mixin::trace, mixin, static_cast<Visitor*>(0));
     Heap::collectGarbage(ThreadState::NoHeapPointersOnStack);
     // The closure should have a persistent handle to the mixin.
     EXPECT_EQ(1, UseMixin::s_traceCount);