Previews should exclude a property if its name is a symbol

src/inspector/injected-script-source.js

Index: src/inspector/injected-script-source.js
diff --git a/src/inspector/injected-script-source.js b/src/inspector/injected-script-source.js
index 044eb736c0243c24acc2e8ee9726a6a07febe297..1ec3850a2f1b9eedc3671b551888aef59de6e910 100644
--- a/src/inspector/injected-script-source.js
+++ b/src/inspector/injected-script-source.js
@@ -943,6 +943,10 @@ InjectedScript.RemoteObject.prototype = {
                 continue;
             }
 
+            // Never preview symbols.
+            if (descriptor.symbol)
+                continue;
+
             var value = descriptor.value;
             var type = typeof value;