Include referrer chain with inline install requests.

chrome/browser/extensions/webstore_standalone_installer.cc

Index: chrome/browser/extensions/webstore_standalone_installer.cc
diff --git a/chrome/browser/extensions/webstore_standalone_installer.cc b/chrome/browser/extensions/webstore_standalone_installer.cc
index 84f1905e3959975cd4237ff408facc824ade74e4..fd7f091c90715af0ad33191d52dc2708cc5ee23c 100644
--- a/chrome/browser/extensions/webstore_standalone_installer.cc
+++ b/chrome/browser/extensions/webstore_standalone_installer.cc
@@ -69,7 +69,7 @@ void WebstoreStandaloneInstaller::BeginInstall() {
       profile_->GetRequestContext(),
       GetRequestorURL(),
       id_));
-  webstore_data_fetcher_->Start();
+  OnBeforeWebstoreDataRequest(webstore_data_fetcher_.get());

[Devlin, 2017/01/27 20:31:34]

(Following up from the other comment)

So here, we'd just do something like:
std::string json_data = GetJsonPostData();
if (!json_data.empty())
  webstore_data_fetcher_->SetJsonPostData(json_data);
webstore_data_fetcher_->Start();

[robertshield, 2017/01/28 03:58:48]

Done.

 }
 
 //
@@ -159,6 +159,11 @@ void WebstoreStandaloneInstaller::InitInstallData(
   // Default implementation sets no properties.
 }
 
+void WebstoreStandaloneInstaller::OnBeforeWebstoreDataRequest(
+    WebstoreDataFetcher* fetcher) {
+  webstore_data_fetcher_->Start();
+}
+
 void WebstoreStandaloneInstaller::OnManifestParsed() {
   ProceedWithInstallPrompt();
 }