Improve error handling of the transport security state generator.

net/tools/transport_security_state_generator/preloaded_state_generator.h

Index: net/tools/transport_security_state_generator/preloaded_state_generator.h
diff --git a/net/tools/transport_security_state_generator/preloaded_state_generator.h b/net/tools/transport_security_state_generator/preloaded_state_generator.h
index 562c4f38ead297ff708d356b45a4399568cb1dad..77a1c97422812772c28048c9258cd520fae63aa6 100644
--- a/net/tools/transport_security_state_generator/preloaded_state_generator.h
+++ b/net/tools/transport_security_state_generator/preloaded_state_generator.h
@@ -28,11 +28,13 @@ class PreloadedStateGenerator {
   PreloadedStateGenerator();
   ~PreloadedStateGenerator();
 
-  std::string Generate(const std::string& preload_template,
-                       const TransportSecurityStateEntries& entries,
-                       const DomainIDList& domain_ids,
-                       const Pinsets& pinsets,
-                       bool verbose);
+  // Generates C++ code and writes it to |*output|. Returns true on success and
+  // false on failure.

[Ryan Sleevi, 2017/02/14 20:53:17]

Why the API signature change? Wouldn't returning an empty string be sufficient
to signal error? Why or why not?

[martijnc, 2017/02/15 22:07:59]

Yes but felt the boolean indicated that a bit better.

Updated to return the empty string on failure.

+  bool Generate(const std::string& preload_template,
+                const TransportSecurityStateEntries& entries,
+                const DomainIDList& domain_ids,
+                const Pinsets& pinsets,
+                std::string* output);
 
  private:
   // TODO(Martijnc): Remove the domain IDs from the preload format.