Add context menu to DataField

Refs vuejs#442

* Adds more actions to dropdown
* Currently adds one item - Copy Value (to clipboard)

Author: crcatala

src/devtools/components/DataField.vue

@@ -111,6 +111,29 @@
             v-tooltip="'Remove value'"
             @click="removeField()"
           />
+          <v-popover
+            popoverClass="context-menu-popover"
+            placement="bottom"
+            :open.sync="contextMenuOpen"
+          >
+            <BaseIcon
+              class="context-field icon-button"
+              icon="more_horiz"
+            />
+          <div
+            slot="popover"
+            class="context-menu"
+            @mouseleave="contextMenuOpen = false"
+          >
+            <div
+              class='context-menu-item'
+              v-close-popover
+              @click='copyToClipboard'
+            >
+              {{ $t('DataField.contextMenu.copyValue') }}
+            </div>
+          </div>
+        </v-popover>
         </span>
       </template>
 
@@ -166,11 +189,13 @@ import {
   isPlainObject,
   sortByKey,
   openInEditor,
+  stringify,
   escape
 } from 'src/util'
 
 import DataFieldEdit from '../mixins/data-field-edit'
 
+
 const rawTypeRE = /^\[object (\w+)]$/
 const specialTypeRE = /^\[native (\w+) (.*)\]$/
 
@@ -184,6 +209,15 @@ function subFieldCount (value) {
   }
 }
 
+function copyToClipboard (state) {
+  const dummyTextArea = document.createElement('textarea')
+  dummyTextArea.textContent = stringify(state)
+  document.body.appendChild(dummyTextArea)
+  dummyTextArea.select()
+  document.execCommand('copy')
+  document.body.removeChild(dummyTextArea)
+}
+
 export default {
   name: 'DataField',
 
@@ -200,6 +234,7 @@ export default {
 
   data () {
     return {
+      contextMenuOpen: false,
       limit: Array.isArray(this.field.value) ? 10 : Infinity,
       expanded: this.depth === 0 && this.field.key !== '$route' && (subFieldCount(this.field.value) < 5)
     }
@@ -378,6 +413,9 @@ export default {
   },
 
   methods: {
+    copyToClipboard () {
+      copyToClipboard(this.field.value)
+    },
     onClick (event) {
       // Cancel if target is interactive
       if (event.target.tagName === 'INPUT' || event.target.className.includes('button')) {
@@ -572,4 +610,19 @@ export default {
 
 .remove-field
   margin-left 10px
+
+.context-menu-item
+  padding 4px 8px
+  cursor pointer
+  background-color transparent
+  &:hover
+    background-color $hover-color
+</style>
+
+<style lang="stylus">
+.popover.context-menu-popover {
+  .popover-inner {
+    padding 6px 0
+  }
+}
 </style>

src/devtools/locales/en.js

@@ -27,6 +27,9 @@ export default {
         tooltip: '[[{{keys.enter}}]] Submit change'
       }
     },
+    contextMenu: {
+      copyValue: 'Copy Value'
+    },
     quickEdit: {
       number: {
         tooltip: `Quick Edit<br><br>