Port visitedlink tests to Linux. Also make them pass on Linux, which

base/shared_memory_win.cc

Index: base/shared_memory_win.cc
diff --git a/base/shared_memory_win.cc b/base/shared_memory_win.cc
index 3822fc94b172439ebbaed9df18f9376bf89d31c2..66f8fb6c94964eb30a7ae3d84ee924e92fe3f181 100644
--- a/base/shared_memory_win.cc
+++ b/base/shared_memory_win.cc
@@ -50,6 +50,11 @@ bool SharedMemory::IsHandleValid(const SharedMemoryHandle& handle) {
   return handle != NULL;
 }
 
+// static
+SharedMemoryHandle SharedMemory::NULLHandle() {
+  return NULL;
+}
+
 bool SharedMemory::Create(const std::wstring &name, bool read_only,
                           bool open_existing, size_t size) {
   DCHECK(mapped_file_ == NULL);