Start using file_util symlink code, now that it's available.

base/file_util_posix.cc

Index: base/file_util_posix.cc
diff --git a/base/file_util_posix.cc b/base/file_util_posix.cc
index e71051eca763f5c51890e10cb04a75d037c8d708..92527c88c0a87e4e2aae9321af5d1062458eb710 100644
--- a/base/file_util_posix.cc
+++ b/base/file_util_posix.cc
@@ -388,11 +388,12 @@ bool ReadSymbolicLink(const FilePath& symlink_path,
   char buf[PATH_MAX];
   ssize_t count = ::readlink(symlink_path.value().c_str(), buf, arraysize(buf));
 
-  if (count <= 0)
+  if (count <= 0) {
+    target_path->clear();
     return false;
+  }
 
   *target_path = FilePath(FilePath::StringType(buf, count));
-
   return true;
 }