Fix a bunch of spelling mistakes :\

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index ba157fe25310704240e6757de21570dbb53c3ce9..f8caa493a228816a66786a7a5b1ef9bb0fe73a5b 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -1904,7 +1904,7 @@ Object* Heap::CopyJSObject(JSObject* source) {
     if (clone->IsFailure()) return clone;
     ASSERT(Heap::InNewSpace(clone));
     // Since we know the clone is allocated in new space, we can copy
-    // the contents without worring about updating the write barrier.
+    // the contents without worrying about updating the write barrier.
     CopyBlock(reinterpret_cast<Object**>(HeapObject::cast(clone)->address()),
               reinterpret_cast<Object**>(source->address()),
               object_size);