Implement the memory mapped file class for posix.

base/file_util.cc

Index: base/file_util.cc
===================================================================
--- base/file_util.cc	(revision 6919)
+++ base/file_util.cc	(working copy)
@@ -275,6 +275,29 @@
   return fclose(file) == 0;
 }
 
+///////////////////////////////////////////////
+// MemoryMappedFile
+
+MemoryMappedFile::~MemoryMappedFile() {
+  CloseHandles();
+}
+
+bool MemoryMappedFile::Initialize(const FilePath& file_name) {
+  if (IsValid())
+    return false;
+
+  if (!MapFileToMemory(file_name)) {
+    CloseHandles();
+    return false;
+  }
+
+  return true;
+}
+
+bool MemoryMappedFile::IsValid() {
+  return data_ != NULL;
+}
+
 // Deprecated functions ----------------------------------------------------
 
 bool AbsolutePath(std::wstring* path_str) {