GN: Makes GN output deterministic

tools/gn/ninja_writer.cc

Index: tools/gn/ninja_writer.cc
diff --git a/tools/gn/ninja_writer.cc b/tools/gn/ninja_writer.cc
index 23b9a72f8f913ff08f1b2ca1b10e430711106795..96ae9355218da926b7499b5dc8fb3a8eeee0bf83 100644
--- a/tools/gn/ninja_writer.cc
+++ b/tools/gn/ninja_writer.cc
@@ -5,11 +5,13 @@
 #include "tools/gn/ninja_writer.h"
 
 #include "tools/gn/builder.h"
+#include "tools/gn/dereference_comparator.h"
 #include "tools/gn/loader.h"
 #include "tools/gn/location.h"
 #include "tools/gn/ninja_build_writer.h"
 #include "tools/gn/ninja_toolchain_writer.h"
 #include "tools/gn/settings.h"
+#include "tools/gn/target.h"
 
 NinjaWriter::NinjaWriter(const BuildSettings* build_settings,
                          Builder* builder)
@@ -30,6 +32,11 @@ bool NinjaWriter::RunAndWriteFiles(const BuildSettings* build_settings,
   std::vector<const Target*> default_targets;
   if (!writer.WriteToolchains(&all_settings, &default_targets, err))
     return false;
+
+  // Sort the targets so that outputs have a consistent order.
+  std::sort(default_targets.begin(), default_targets.end(),
+            DereferenceComparator<Target>());
+
   return writer.WriteRootBuildfiles(all_settings, default_targets, err);
 }
 
@@ -70,13 +77,14 @@ bool NinjaWriter::WriteToolchains(std::vector<const Settings*>* all_settings,
 
   // Write out the toolchain buildfiles, and also accumulate the set of
   // all settings and find the list of targets in the default toolchain.
-  for (CategorizedMap::const_iterator i = categorized.begin();
-       i != categorized.end(); ++i) {
+  for (CategorizedMap::iterator i = categorized.begin(); i != categorized.end();
+       ++i) {
     const Settings* settings =
         builder_->loader()->GetToolchainSettings(i->first);
     const Toolchain* toolchain = builder_->GetToolchain(i->first);
 
     all_settings->push_back(settings);
+
     if (!NinjaToolchainWriter::RunAndWriteFile(settings, toolchain,
                                                i->second)) {
       Err(Location(),