Add <eval-link> - a custom element for evaluating an expression.

runtime/bin/vmservice/client/lib/src/elements/instance_view.html

Index: runtime/bin/vmservice/client/lib/src/elements/instance_view.html
diff --git a/runtime/bin/vmservice/client/lib/src/elements/instance_view.html b/runtime/bin/vmservice/client/lib/src/elements/instance_view.html
index f89a371e9a80ca5c6e94885dec9c7d70b2c034be..8ac78ff482dae46424c3fa1686ee4d745f7d5e1c 100644
--- a/runtime/bin/vmservice/client/lib/src/elements/instance_view.html
+++ b/runtime/bin/vmservice/client/lib/src/elements/instance_view.html
@@ -90,6 +90,15 @@
               </div>
             </div>
           </template>
+
+          <div class="memberItem">&nbsp;</div>
+
+          <div class="memberItem">
+            <div class="memberName">toString()</div>
+            <div class="memberValue">
+              <eval-link callback="{{ eval }}" expr="toString()"></eval-link>
+            </div>
+          </div>
         </div>
       </div>