[GN] Don't rewrite files with the same contents

tools/gn/function_write_file.cc

Index: tools/gn/function_write_file.cc
diff --git a/tools/gn/function_write_file.cc b/tools/gn/function_write_file.cc
index 91599755a37e239ec3a4a155a8c46fb7459eda6b..eeba89a7f3d9a673cc98e181ca150a54322b266f 100644
--- a/tools/gn/function_write_file.cc
+++ b/tools/gn/function_write_file.cc
@@ -130,7 +130,7 @@ Value RunWriteFile(Scope* scope,
       scope->settings()->build_settings()->GetFullPath(source_file));
 
   // Compute output.
-  std::ostringstream contents;
+  std::stringstream contents;
   if (args[1].type() == Value::LIST) {
     const std::vector<Value>& list = args[1].list_value();
     for (const auto& cur : list)
@@ -138,14 +138,12 @@ Value RunWriteFile(Scope* scope,
   } else {
     contents << args[1].ToString(false);
   }
-  const std::string& new_contents = contents.str();
+
   base::FilePath file_path =
       scope->settings()->build_settings()->GetFullPath(source_file);
 
   // Make sure we're not replacing the same contents.
-  std::string existing_contents;
-  if (base::ReadFileToString(file_path, &existing_contents) &&
-      existing_contents == new_contents)
+  if (ContentsEqual(file_path, &contents))
     return Value();  // Nothing to do.
 
   // Write file, creating the directory if necessary.

[brettw, 2016/02/02 20:50:23]

Can the rest of this function and DoWriteFile all be merged into
WriteFileIfChanged?

[Tomasz Moniuszko, 2016/02/03 10:20:30]

Done.

@@ -155,6 +153,7 @@ Value RunWriteFile(Scope* scope,
     return Value();
   }
 
+  const std::string& new_contents = contents.str();
   int int_size = static_cast<int>(new_contents.size());
   if (DoWriteFile(file_path, new_contents.c_str(), int_size)
       != int_size) {