[DevTools] Address crash by checking if Tab loaded successfully

chrome/browser/android/dev_tools_manager_delegate_android.cc

Index: chrome/browser/android/dev_tools_manager_delegate_android.cc
diff --git a/chrome/browser/android/dev_tools_manager_delegate_android.cc b/chrome/browser/android/dev_tools_manager_delegate_android.cc
index 2754946b111ee5b9eabf1f5ecda21f9c47e7398f..d4f6631e9aef6422850e12bf899db7f355c7e988 100644
--- a/chrome/browser/android/dev_tools_manager_delegate_android.cc
+++ b/chrome/browser/android/dev_tools_manager_delegate_android.cc
@@ -140,7 +140,9 @@ class TabTarget : public TargetBase {
       if (!tab)
         return NULL;
 
-      tab->LoadIfNeeded();
+      if (!tab->LoadIfNeeded())
+        return NULL;
+
       web_contents = model->GetWebContentsAt(index);
       if (!web_contents)
         return NULL;