Add copy button to share dialog

copy-button.diff

diff --git a/src/sidebar/components/share-dialog.js b/src/sidebar/components/share-dialog.js
index 652d1b8d..534597e4 100644
--- a/src/sidebar/components/share-dialog.js
+++ b/src/sidebar/components/share-dialog.js
@@ -2,6 +2,21 @@
 
 var VIA_PREFIX = 'https://via.hypothes.is/';
 
+function copyToClipboard(text) {
+  // Temporarily add a hidden input element and populate it with the text we
+  // want to copy.
+  var inputEl = document.createElement('textarea');
+  document.body.appendChild(inputEl);
+  inputEl.textContent = text;
+  inputEl.focus();
+  inputEl.selectionStart = 0;
+  inputEl.selectionEnd = text.length;
+
+  document.execCommand('copy');
+
+  inputEl.remove();
+}
+
 // @ngInject
 function ShareDialogController($scope, $element, analytics, annotationUI) {
   var self = this;
@@ -32,6 +47,13 @@ function ShareDialogController($scope, $element, analytics, annotationUI) {
       analytics.track(analytics.events.DOCUMENT_SHARED, target);
     }
   };
+
+  $scope.copyAnnotations = function () {
+    var annotations = annotationUI.getState().annotations;
+    var content = annotations.map(ann => ann.text).join('\n\n');
+
+    copyToClipboard(content);
+  };
 }
 
 module.exports = {
diff --git a/src/sidebar/templates/share-dialog.html b/src/sidebar/templates/share-dialog.html
index 1bf4438c..af497bd7 100644
--- a/src/sidebar/templates/share-dialog.html
+++ b/src/sidebar/templates/share-dialog.html
@@ -35,6 +35,7 @@
          class="share-link-icon h-icon-mail"
          ng-click="onShareClick('email')"></a>
       </p>
+      <button ng-click="copyAnnotations()">Copy annotations</button>
     </div>
   </div>
 </div>