Add feedback icon for plugin use

Change-Id: Ie6ba10f64dfc8e1052070ee57ba26722ae1ce2e6

polygerrit-ui/app/elements/shared/gr-icons/gr-icons.ts

diff --git a/polygerrit-ui/app/elements/shared/gr-icons/gr-icons.ts b/polygerrit-ui/app/elements/shared/gr-icons/gr-icons.ts
index ccaa33c..69573c7 100644
--- a/polygerrit-ui/app/elements/shared/gr-icons/gr-icons.ts
+++ b/polygerrit-ui/app/elements/shared/gr-icons/gr-icons.ts
@@ -156,6 +156,8 @@
       <g id="file-present"><path d="M0 0h24v24H0V0z" fill="none"/><path d="M15 2H6c-1.1 0-2 .9-2 2v16c0 1.1.9 2 2 2h12c1.1 0 2-.9 2-2V7l-5-5zM6 20V4h8v4h4v12H6zm10-10v5c0 2.21-1.79 4-4 4s-4-1.79-4-4V8.5c0-1.47 1.26-2.64 2.76-2.49 1.3.13 2.24 1.32 2.24 2.63V15h-2V8.5c0-.28-.22-.5-.5-.5s-.5.22-.5.5V15c0 1.1.9 2 2 2s2-.9 2-2v-5h2z"/></g>
       <!-- This SVG is a copy from material.io https://fonts.google.com/icons?selected=Material%20Icons%3Aarrow_forward-->
       <g id="arrow-forward"><path d="M0 0h24v24H0z" fill="none"/><path d="M12 4l-1.41 1.41L16.17 11H4v2h12.17l-5.58 5.59L12 20l8-8z"/></g>
+      <!-- This SVG is a copy from material.io https://fonts.google.com/icons?selected=Material+Icons:feedback -->
+      <g id="feedback"><path d="M0 0h24v24H0z" fill="none"/><path d="M20 2H4c-1.1 0-1.99.9-1.99 2L2 22l4-4h14c1.1 0 2-.9 2-2V4c0-1.1-.9-2-2-2zm-7 12h-2v-2h2v2zm0-4h-2V6h2v4z"/></g>
     </defs>
   </svg>
 </iron-iconset-svg>`;