Bug 1383299 - Ensure we start to set up network connection before content process requests. r=mconley

In chrome process, we often know which url is going to be loaded.
As a performance optimization, we can start initiating network
connection before sending out the 'LoadURI' message to the content
process.

MozReview-Commit-ID: L79ylHOaxX8

--HG--
extra : rebase_source : cc3aeefedde21dc8eaaf37c67710980b0204f4dc

toolkit/components/remotebrowserutils/RemoteWebNavigation.js

@@ -13,6 +13,8 @@ XPCOMUtils.defineLazyModuleGetter(this, "NetUtil",
   "resource://gre/modules/NetUtil.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "Utils",
   "resource://gre/modules/sessionstore/Utils.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "PrivateBrowsingUtils",
+  "resource://gre/modules/PrivateBrowsingUtils.jsm");
 
 function makeURI(url) {
   return Services.io.newURI(url);
@@ -72,6 +74,29 @@ RemoteWebNavigation.prototype = {
   },
   loadURIWithOptions(aURI, aLoadFlags, aReferrer, aReferrerPolicy,
                      aPostData, aHeaders, aBaseURI, aTriggeringPrincipal) {
+    // We know the url is going to be loaded, let's start requesting network
+    // connection before the content process asks.
+    // Note that we might have already setup the speculative connection in some
+    // cases, especially when the url is from location bar or its popup menu.
+    if (aURI.startsWith("http")) {
+      let uri = makeURI(aURI);
+      let principal = aTriggeringPrincipal;
+      // We usually have a aTriggeringPrincipal assigned, but in case we don't
+      // have one, create it with OA inferred from the current context.
+      if (!principal) {
+        let attrs = {
+          userContextId: this._browser.getAttribute("usercontextid") || 0,
+          privateBrowsingId: PrivateBrowsingUtils.isBrowserPrivate(this._browser) ? 1 : 0
+        };
+        principal = Services.scriptSecurityManager.createCodebasePrincipal(uri, attrs);
+      }
+      try {
+        Services.io.speculativeConnect2(uri, principal, null);
+      } catch (ex) {
+        // Can't setup speculative connection for this uri string for some
+        // reason, just ignore it.
+      }
+    }
     this._sendMessage("WebNavigation:LoadURI", {
       uri: aURI,
       flags: aLoadFlags,