[Blimp Client] Fixes up URL before sending it to Engine.

blimp/engine/session/blimp_engine_session.cc

Index: blimp/engine/session/blimp_engine_session.cc
diff --git a/blimp/engine/session/blimp_engine_session.cc b/blimp/engine/session/blimp_engine_session.cc
index 32cfcd52bdb11113fa5b4913800b6e4e1a77d5aa..4babcbc6827d99be9c26c81f36320ac536087583 100644
--- a/blimp/engine/session/blimp_engine_session.cc
+++ b/blimp/engine/session/blimp_engine_session.cc
@@ -321,7 +321,8 @@ void BlimpEngineSession::HandleResize(float device_pixel_ratio,
 
 void BlimpEngineSession::LoadUrl(const int target_tab_id, const GURL& url) {
   DVLOG(1) << "Load URL " << url << " in tab " << target_tab_id;
-  if (url.is_empty()) {
+  if (!url.is_valid()) {
+    VLOG(1) << "Dropping invalid URL " << url;
     return;
   }