GN: don't write separate files for non-binary targets

tools/gn/ninja_target_writer.h

Index: tools/gn/ninja_target_writer.h
diff --git a/tools/gn/ninja_target_writer.h b/tools/gn/ninja_target_writer.h
index 0248b0788d765a07deb390f986527fffd4db5a6d..fd781ead19413a547eec23293ba5286bcbb8d064 100644
--- a/tools/gn/ninja_target_writer.h
+++ b/tools/gn/ninja_target_writer.h
@@ -24,7 +24,14 @@ class NinjaTargetWriter {
   NinjaTargetWriter(const Target* target, std::ostream& out);
   virtual ~NinjaTargetWriter();
 
-  static void RunAndWriteFile(const Target* target);
+  // Returns the build line to be written to the toolchain build file.
+  //
+  // Some targets have their rules get written to separate files, and some

[brucedawson, 2016/07/25 17:38:00]

"rules get written" -> "rules written"

+  // can have their rules coalesced in the main build file. For the coalesced
+  // case, this function will return the rules as a string. For the separate
+  // file case, the separate ninja file will be written and the return string
+  // will be the subninja command to load that file.
+  static std::string RunAndWriteFile(const Target* target);
 
   virtual void Run() = 0;