[Blimp] Refactor Blimp test engine with embedded test server and URL rewriting

blimp/engine/app/blimp_content_main_delegate.cc

Index: blimp/engine/app/blimp_content_main_delegate.cc
diff --git a/blimp/engine/app/blimp_content_main_delegate.cc b/blimp/engine/app/blimp_content_main_delegate.cc
index 5cfa4c8b509ce5ccf3dc3bc527d886a8c8803874..3d6429c5e4667fcb496dd9745f2b1537d2968b71 100644
--- a/blimp/engine/app/blimp_content_main_delegate.cc
+++ b/blimp/engine/app/blimp_content_main_delegate.cc
@@ -78,6 +78,11 @@ void BlimpContentMainDelegate::InitializeResourceBundle() {
   ui::ResourceBundle::InitSharedInstanceWithPakPath(pak_file);
 }
 
+void BlimpContentMainDelegate::SetContentBrowserClientForTesting(
+    std::unique_ptr<BlimpContentBrowserClient> browser_client_ptr) {
+  browser_client_ = std::move(browser_client_ptr);
+}
+
 content::ContentBrowserClient*
 BlimpContentMainDelegate::CreateContentBrowserClient() {
   DCHECK(!browser_client_);