Fix issue where “Click to add topic” was being cut off

+ Moves the max-width property outside of the gr-editable-label
  component since that should be set by the owner.
+ Increases max-width so that the placeholder text isn’t cut off.

Change-Id: Ife9e13c5f0c06908e05b2580b01b7612e14598f0

polygerrit-ui/app/elements/change/gr-change-metadata/gr-change-metadata.html

@@ -37,6 +37,9 @@ limitations under the License.
         color: #666;
         font-weight: bold;
       }
+      gr-editable-label {
+        max-width: 9em;
+      }
       .labelValueContainer:not(:first-of-type) {
         margin-top: .25em;
       }

polygerrit-ui/app/elements/shared/gr-editable-label/gr-editable-label.html

@@ -18,14 +18,19 @@ limitations under the License.
 <dom-module id="gr-editable-label">
   <template>
     <style>
+      :host {
+        display: inline-block;
+      }
+      input,
+      label {
+        width: 100%;
+      }
       input {
         font: inherit;
-        max-width: 8em;
       }
       label {
         color: #777;
         display: inline-block;
-        max-width: 8em;
         overflow: hidden;
         text-overflow: ellipsis;
         white-space: nowrap;