[geary/wip/728002-webkit2] Don't send JS selectionChanged message unless param value has changed.

[Michael Gratton <mjog src gnome org>]

commit 7455bf6ada78d29085a8fd5ed97e5aa0e090258f
Author: Michael James Gratton <mike vee net>
Date:   Thu Jan 19 01:58:26 2017 +1100

    Don't send JS selectionChanged message unless param value has changed.

 src/client/web-process/web-process-extension.vala |    4 ++++
 ui/client-web-view.js                             |    6 +++++-
 2 files changed, 9 insertions(+), 1 deletions(-)
---
diff --git a/src/client/web-process/web-process-extension.vala 
b/src/client/web-process/web-process-extension.vala
index 1b4980b..2fc4067 100644
--- a/src/client/web-process/web-process-extension.vala
+++ b/src/client/web-process/web-process-extension.vala
@@ -39,6 +39,10 @@ public class GearyWebExtension : Object {
         extension.page_created.connect((extension, web_page) => {
                 web_page.console_message_sent.connect(on_console_message);
                 web_page.send_request.connect(on_send_request);
+                // XXX investigate whether the earliest supported
+                // version of WK supports the DOM "selectionchanged"
+                // event, and if so use that rather that doing it in
+                // here in the extension
                 web_page.get_editor().selection_changed.connect(() => {
                     selection_changed(web_page);
                 });
diff --git a/ui/client-web-view.js b/ui/client-web-view.js
index eb87c2f..ba224ae 100644
--- a/ui/client-web-view.js
+++ b/ui/client-web-view.js
@@ -16,6 +16,7 @@ PageState.prototype = {
     init: function() {
         this.allowRemoteImages = false;
         this.isLoaded = false;
+        this.hasSelection = false;
 
         let state = this;
         let timeoutId = window.setInterval(function() {
@@ -54,6 +55,9 @@ PageState.prototype = {
     },
     selectionChanged: function() {
         let hasSelection = !window.getSelection().isCollapsed;
-        window.webkit.messageHandlers.selectionChanged.postMessage(hasSelection);
+        if (this.hasSelection != hasSelection) {
+            this.hasSelection = hasSelection;
+            window.webkit.messageHandlers.selectionChanged.postMessage(hasSelection);
+        }
     }
 };