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

tools/gn/visual_studio_writer.cc

Index: tools/gn/visual_studio_writer.cc
diff --git a/tools/gn/visual_studio_writer.cc b/tools/gn/visual_studio_writer.cc
index 968e046b72fb129979ea276b5fe8cb0f5cc0aabb..c23db55398e6099d530de76505af085e31f05457 100644
--- a/tools/gn/visual_studio_writer.cc
+++ b/tools/gn/visual_studio_writer.cc
@@ -9,7 +9,6 @@
 #include <set>
 #include <string>
 
-#include "base/files/file_util.h"
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/strings/string_util.h"
@@ -153,26 +152,6 @@ base::StringPiece FindParentDir(const std::string* path) {
   return base::StringPiece();
 }
 
-bool HasSameContent(std::stringstream& data_1, const base::FilePath& data_2) {
-  // Compare file sizes first. Quick and will save us some time if they are
-  // different sizes.
-  int64_t data_1_len = data_1.tellp();
-
-  int64_t data_2_len;
-  if (!base::GetFileSize(data_2, &data_2_len) || data_1_len != data_2_len)
-    return false;
-
-  std::string data_2_data;
-  data_2_data.resize(data_2_len);
-  if (!base::ReadFileToString(data_2, &data_2_data))
-    return false;
-
-  std::string data_1_data;
-  data_1_data = data_1.str();
-
-  return data_1_data == data_2_data;
-}
-
 }  // namespace
 
 VisualStudioWriter::SolutionEntry::SolutionEntry(const std::string& _name,
@@ -265,14 +244,10 @@ bool VisualStudioWriter::WriteProjectFiles(const Target* target, Err* err) {
   // Only write the content to the file if it's different. That is
   // both a performance optimization and more importantly, prevents
   // Visual Studio from reloading the projects.
-  if (!HasSameContent(vcxproj_string_out, vcxproj_path)) {
-    std::string content = vcxproj_string_out.str();
-    int size = static_cast<int>(content.size());
-    if (base::WriteFile(vcxproj_path, content.c_str(), size) != size) {
-      *err = Err(Location(), "Couldn't open " + target->label().name() +
-                                 ".vcxproj for writing");
-      return false;
-    }
+  if (!WriteFileIfChanged(vcxproj_path, &vcxproj_string_out)) {
+    *err = Err(Location(),
+               "Couldn't write " + target->label().name() + ".vcxproj");
+    return false;
   }
 
   base::FilePath filters_path = UTF8ToFilePath(vcxproj_path_str + ".filters");
@@ -280,14 +255,9 @@ bool VisualStudioWriter::WriteProjectFiles(const Target* target, Err* err) {
   std::stringstream filters_string_out;
   WriteFiltersFileContents(filters_string_out, target);
 
-  if (!HasSameContent(filters_string_out, filters_path)) {
-    std::string content = filters_string_out.str();
-    int size = static_cast<int>(content.size());
-    if (base::WriteFile(filters_path, content.c_str(), size) != size) {
-      *err = Err(Location(), "Couldn't open " + target->label().name() +
-                                 ".vcxproj.filters for writing");
-      return false;
-    }
+  if (!WriteFileIfChanged(filters_path, &filters_string_out)) {
+    *err = Err(Location(),
+               "Couldn't write " + target->label().name() + ".vcxproj.filters");
   }
 
   return true;
@@ -586,13 +556,8 @@ bool VisualStudioWriter::WriteSolutionFile(Err* err) {
   // Only write the content to the file if it's different. That is
   // both a performance optimization and more importantly, prevents
   // Visual Studio from reloading the projects.
-  if (HasSameContent(string_out, sln_path))
-    return true;
-
-  std::string content = string_out.str();
-  int size = static_cast<int>(content.size());
-  if (base::WriteFile(sln_path, content.c_str(), size) != size) {
-    *err = Err(Location(), "Couldn't open all.sln for writing");
+  if (!WriteFileIfChanged(sln_path, &string_out)) {
+    *err = Err(Location(), "Couldn't write all.sln");
     return false;
   }