Fix crashers and issues when rendering blimp in tabs

blimp/client/core/render_widget/render_widget_feature.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "blimp/client/core/render_widget/render_widget_feature.h"
 
 #include "base/numerics/safe_conversions.h"
 #include "blimp/common/create_blimp_message.h"
 #include "blimp/common/proto/blimp_message.pb.h"
 #include "blimp/common/proto/compositor.pb.h"
@@ skipping 70 matching lines @@
 
 void RenderWidgetFeature::ProcessMessage(
     std::unique_ptr<BlimpMessage> message,
     const net::CompletionCallback& callback) {
   DCHECK(!callback.is_null());
   DCHECK(BlimpMessage::kRenderWidget == message->feature_case() ||
          BlimpMessage::kCompositor == message->feature_case());
 
   int target_tab_id = message->target_tab_id();
   RenderWidgetFeatureDelegate* delegate = FindDelegate(target_tab_id);
-  DCHECK(delegate) << "RenderWidgetFeatureDelegate not found for "
-                   << target_tab_id;
+  if (!delegate) {
+    VLOG(1) << "RenderWidgetFeatureDelegate not found for " << target_tab_id
+            << ". Ignoring.";
+    callback.Run(net::OK);
+    return;
+  }
 
   switch (message->feature_case()) {
     case BlimpMessage::kRenderWidget:
       ProcessRenderWidgetMessage(delegate, message->render_widget());
       break;
     case BlimpMessage::kCompositor:
       ProcessCompositorMessage(delegate, message->compositor());
       break;
     default:
       NOTREACHED();
@@ skipping 39 matching lines @@
 RenderWidgetFeature::RenderWidgetFeatureDelegate*
 RenderWidgetFeature::FindDelegate(const int tab_id) {
   DelegateMap::const_iterator it = delegates_.find(tab_id);
   if (it != delegates_.end())
     return it->second;
   return nullptr;
 }
 
 }  // namespace client
 }  // namespace blimp