Add a flag to bssl client to enable False Start.

One more flag we'd need for bssl client to mimic Chromium.

Change-Id: I66bb43f0d6789c8ab922679747b7e9bc28c1d849
Reviewed-on: https://boringssl-review.googlesource.com/5010
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/tool/client.cc b/tool/client.cc
index 1de0df2..9f25eea 100644
--- a/tool/client.cc
+++ b/tool/client.cc
@@ -70,6 +70,10 @@
      "The key to use for signing a channel ID",
     },
     {
+     "-false-start", kBooleanArgument,
+     "Enable False Start",
+    },
+    {
      "", kOptionalArgument, "",
     },
 };
@@ -214,6 +218,10 @@
     ctx->tlsext_channel_id_enabled_new = 1;
   }
 
+  if (args_map.count("-false-start") != 0) {
+    SSL_CTX_set_mode(ctx.get(), SSL_MODE_ENABLE_FALSE_START);
+  }
+
   int sock = -1;
   if (!Connect(&sock, args_map["-connect"])) {
     return false;