waitTask should survive cross-process navigation (#435)

In case of cross-process navigation, we receive a context
which is immediately getting destroyed.

Fixes #396.

lib/FrameManager.js

@@ -419,6 +419,11 @@ class WaitTask {
     if (error && error.message.includes('Execution context was destroyed'))
       return;
 
+    // We could have tried to evaluate in a context which was already
+    // destroyed.
+    if (error && error.message.includes('Cannot find context with specified id'))
+      return;
+
     if (error)
       this._reject(error);
     else