[Blimp] Adds blimp engine browser test framework and LoadUrl test.

blimp/engine/app/blimp_browser_main_parts.cc

Index: blimp/engine/app/blimp_browser_main_parts.cc
diff --git a/blimp/engine/app/blimp_browser_main_parts.cc b/blimp/engine/app/blimp_browser_main_parts.cc
index c37d2cd0bacad638af315a1195226a7ff9a3eac1..7ce6201d9113b02e76664905975cbf4e7268c36f 100644
--- a/blimp/engine/app/blimp_browser_main_parts.cc
+++ b/blimp/engine/app/blimp_browser_main_parts.cc
@@ -60,5 +60,9 @@ SettingsManager* BlimpBrowserMainParts::GetSettingsManager() {
   return settings_manager_.get();
 }
 
+BlimpEngineSession* BlimpBrowserMainParts::GetBlimpEngineSession() {
+  return engine_session_.get();
+}
+
 }  // namespace engine
 }  // namespace blimp