Issue 5013 - Make parameter const ref when applicable.

src/DefaultFileSystem.cpp

Index: src/DefaultFileSystem.cpp
===================================================================
--- a/src/DefaultFileSystem.cpp
+++ b/src/DefaultFileSystem.cpp
@@ -71,20 +71,20 @@
 {
   std::shared_ptr<std::istream> result(new std::ifstream(NormalizePath(path).c_str()));
   if (result->fail())
     throw RuntimeErrorWithErrno("Failed to open " + path);
   return result;
 }
 
 void DefaultFileSystem::Write(const std::string& path,
-                              std::shared_ptr<std::istream> data)
+                              const std::istream& data)
 {
   std::ofstream file(NormalizePath(path).c_str(), std::ios_base::out | std::ios_base::binary);
-  file << Utils::Slurp(*data);
+  file << Utils::Slurp(data);
 }
 
 void DefaultFileSystem::Move(const std::string& fromPath,
                              const std::string& toPath)
 {
   if (rename(NormalizePath(fromPath).c_str(), NormalizePath(toPath).c_str()))
     throw RuntimeErrorWithErrno("Failed to move " + fromPath + " to " + toPath);
 }