[headless] Use version for product name and user agent.

headless/lib/headless_content_client.cc

Index: headless/lib/headless_content_client.cc
diff --git a/headless/lib/headless_content_client.cc b/headless/lib/headless_content_client.cc
index 4269da62f0d21339e3bd71dcf43cf51609deacb3..333f43a6ac95189ee3ad140a973eac9314ad3c8e 100644
--- a/headless/lib/headless_content_client.cc
+++ b/headless/lib/headless_content_client.cc
@@ -14,6 +14,10 @@ HeadlessContentClient::HeadlessContentClient(HeadlessBrowser::Options* options)
 
 HeadlessContentClient::~HeadlessContentClient() {}
 
+std::string HeadlessContentClient::GetProduct() const {
+  return options_->product_name_and_version;
+}
+
 std::string HeadlessContentClient::GetUserAgent() const {
   return options_->user_agent;
 }