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/1068946Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#565076}

third_party/blink/renderer/devtools/front_end/externs.js

@@ -1027,3 +1027,17 @@ DetailsRenderer.NodeDetailsJSON;
  * }}
  */
 DetailsRenderer.OpportunitySummary;
+
+
+// Clipboard API
+
+/** @constructor */
+const Clipboard = function() {};
+/**
+ * @param {string} data
+ * @return {!Promise}
+ */
+Clipboard.prototype.writeText = function(data) {};
+
+/** @type {Clipboard} */
+Navigator.prototype.clipboard;

third_party/blink/renderer/devtools/front_end/host/InspectorFrontendHost.js

@@ -157,9 +157,21 @@ Host.InspectorFrontendHostStub = class {
   /**
    * @override
    * @param {string} text
+   * @suppressGlobalPropertiesCheck
    */
   copyText(text) {
-    Common.console.error('Clipboard is not enabled in hosted mode. Please inspect using chrome://inspect');
+    if (navigator.clipboard) {
+      navigator.clipboard.writeText(text);
+    } else if (document.queryCommandSupported('copy')) {
+      const input = document.createElement('input');
+      input.value = text;
+      document.body.appendChild(input);
+      input.select();
+      document.execCommand('copy');
+      document.body.removeChild(input);
+    } else {
+      Common.console.error('Clipboard is not enabled in hosted mode. Please inspect using chrome://inspect');
+    }
   }
 
   /**