Enable copyText in hosted mode

Now that new clipboard API is available in stable Chrome, it can be used
to enable copy actions by default even in hosted mode.

Change-Id: Ifacb15f7db990c03df21f97560a6e81e9b7746f0
Reviewed-on: https://chromium-review.googlesource.com/1068946
Reviewed-by: Dmitry Gozman <[email protected]>
Commit-Queue: Dmitry Gozman <[email protected]>
Cr-Original-Commit-Position: refs/heads/master@{#565076}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 831241e74851285dbd9a0562e86f0f9b9f674887
diff --git a/front_end/externs.js b/front_end/externs.js
index 19bc4f0..ae58b8b 100644
--- a/front_end/externs.js
+++ b/front_end/externs.js
@@ -1027,3 +1027,17 @@
  * }}
  */
 DetailsRenderer.OpportunitySummary;
+
+
+// Clipboard API
+
+/** @constructor */
+const Clipboard = function() {};
+/**
+ * @param {string} data
+ * @return {!Promise}
+ */
+Clipboard.prototype.writeText = function(data) {};
+
+/** @type {Clipboard} */
+Navigator.prototype.clipboard;