Revert "Remove the Social API"

browser/base/content/content.js

@@ -698,6 +698,37 @@ var PageMetadataMessenger = {
 }
 PageMetadataMessenger.init();
 
+addEventListener("ActivateSocialFeature", function (aEvent) {
+  let document = content.document;
+  let dwu = content.QueryInterface(Ci.nsIInterfaceRequestor)
+                   .getInterface(Ci.nsIDOMWindowUtils);
+  if (!dwu.isHandlingUserInput) {
+    Cu.reportError("attempt to activate provider without user input from " + document.nodePrincipal.origin);
+    return;
+  }
+
+  let node = aEvent.target;
+  let ownerDocument = node.ownerDocument;
+  let data = node.getAttribute("data-service");
+  if (data) {
+    try {
+      data = JSON.parse(data);
+    } catch (e) {
+      Cu.reportError("Social Service manifest parse error: " + e);
+      return;
+    }
+  } else {
+    Cu.reportError("Social Service manifest not available");
+    return;
+  }
+
+  sendAsyncMessage("Social:Activation", {
+    url: ownerDocument.location.href,
+    origin: ownerDocument.nodePrincipal.origin,
+    manifest: data
+  });
+}, true, true);
+
 addMessageListener("ContextMenu:SaveVideoFrameAsImage", (message) => {
   let video = message.objects.target;
   let canvas = content.document.createElementNS("http://www.w3.org/1999/xhtml", "canvas");