Add a key purpose parameter to Certificate PathBuilder.

net/tools/cert_verify_tool/cert_verify_tool.cc

Index: net/tools/cert_verify_tool/cert_verify_tool.cc
diff --git a/net/tools/cert_verify_tool/cert_verify_tool.cc b/net/tools/cert_verify_tool/cert_verify_tool.cc
index 78e10bfa86297c19738b3e8b32fd0ae75142fca4..55753364624c0137195a172eb6a4d3d7e8b8fe2c 100644
--- a/net/tools/cert_verify_tool/cert_verify_tool.cc
+++ b/net/tools/cert_verify_tool/cert_verify_tool.cc
@@ -126,6 +126,8 @@ int main(int argc, char** argv) {
     return 1;
   }
 
+  // TODO(eroman): Also use CertVerifyProcBuiltin.
+
   std::cout << "CertVerifyProc:\n";
   bool cert_verify_proc_ok = true;
   if (!time_flag.empty()) {