Bug 1379117 Part 1: MOZ_ASSERT when not retrieving nsIWebBrowserPrint through docshell for Print Preview. r=jwatt

Changing the last retrieval of the nsIWebBrowserPrint in
printpreview_bug396024_helper.xul caused problems because doing it via the
docshell interrupts the load that triggers run5.
So, I moved the test to run5, which is more consistent with run2 and run3.
I then realised that the frames would have switched anyway, so I changed it to
retrieve frame[0] for the last test, which I think makes more sense.
It's not totally clear to me what this was testing originally or whether it
continued to do so after the addition of the second iframe a long time ago.

layout/base/nsDocumentViewer.cpp

@@ -3946,9 +3946,8 @@ nsDocumentViewer::PrintPreview(nsIPrintSettings* aPrintSettings,
                                nsIWebProgressListener* aWebProgressListener)
 {
 #if defined(NS_PRINTING) && defined(NS_PRINT_PREVIEW)
-  NS_WARNING_ASSERTION(
-    IsInitializedForPrintPreview(),
-    "Using docshell.printPreview is the preferred way for print previewing!");
+  MOZ_ASSERT(IsInitializedForPrintPreview(),
+    "For print preview nsIWebBrowserPrint must be from docshell.printPreview!");
 
   NS_ENSURE_ARG_POINTER(aChildDOMWin);
   nsresult rv = NS_OK;

layout/base/tests/chrome/printpreview_bug396024_helper.xul

@@ -17,8 +17,7 @@ var todo = window.opener.wrappedJSObject.todo;
 var SimpleTest = window.opener.wrappedJSObject.SimpleTest;
 var gWbp;
 function printpreview() {
-  gWbp = window.frames[1].QueryInterface(Components.interfaces.nsIInterfaceRequestor)
-             .getInterface(Components.interfaces.nsIWebBrowserPrint);
+  gWbp = window.frames[1].document.docShell.printPreview;
   var listener = {
     onLocationChange: function(webProgress, request, location, flags) { },
     onProgressChange: function(webProgress, request, curSelfProgress, 
@@ -44,8 +43,7 @@ function printpreview() {
 }
 
 function exitprintpreview() {
-  window.frames[1].QueryInterface(Components.interfaces.nsIInterfaceRequestor)
-   .getInterface(Components.interfaces.nsIWebBrowserPrint).exitPrintPreview(); 
+  window.frames[1].document.docShell.printPreview.exitPrintPreview();
 }
 
 function finish() {
@@ -91,8 +89,7 @@ function run2() {
 }
 
 function run3() {
-  gWbp = window.frames[1].QueryInterface(Components.interfaces.nsIInterfaceRequestor)
-             .getInterface(Components.interfaces.nsIWebBrowserPrint);
+  gWbp = window.frames[1].document.docShell.printPreview;
   ok(gWbp.doingPrintPreview, "Should be doing print preview");
   exitprintpreview();
   setTimeout(run4, 0);
@@ -108,12 +105,12 @@ function run4() {
   i.addEventListener("load", loadhandler, true);
   document.documentElement.getBoundingClientRect();
   document.documentElement.appendChild(i);
-  gWbp = window.frames[1].QueryInterface(Components.interfaces.nsIInterfaceRequestor)
-             .getInterface(Components.interfaces.nsIWebBrowserPrint);
-  ok(!gWbp.doingPrintPreview, "Should not be doing print preview anymore2");
 }
 
 function run5() {
+  gWbp = window.frames[0].document.docShell.printPreview;
+  ok(!gWbp.doingPrintPreview, "Should not be doing print preview anymore2");
+
   //XXX this shouldn't be necessary, see bug 405555
   printpreview();
   exitprintpreview();

layout/base/tests/chrome/printpreview_bug482976_helper.xul

@@ -17,8 +17,7 @@ var todo = window.opener.wrappedJSObject.todo;
 var SimpleTest = window.opener.wrappedJSObject.SimpleTest;
 var gWbp;
 function printpreview() {
-  gWbp = window.frames[1].QueryInterface(Components.interfaces.nsIInterfaceRequestor)
-             .getInterface(Components.interfaces.nsIWebBrowserPrint);
+  gWbp = window.frames[1].document.docShell.printPreview;
   var listener = {
     onLocationChange: function(webProgress, request, location, flags) { },
     onProgressChange: function(webProgress, request, curSelfProgress, 
@@ -44,8 +43,7 @@ function printpreview() {
 }
 
 function exitprintpreview() {
-  window.frames[1].QueryInterface(Components.interfaces.nsIInterfaceRequestor)
-   .getInterface(Components.interfaces.nsIWebBrowserPrint).exitPrintPreview(); 
+  window.frames[1].document.docShell.printPreview.exitPrintPreview();
 }
 
 function finish() {

layout/base/tests/chrome/printpreview_helper.xul

@@ -24,8 +24,7 @@ var file = Components.classes["@mozilla.org/file/directory_service;1"]
 filePath = file.path;
 
 function printpreview() {
-  gWbp = window.frames[1].QueryInterface(Components.interfaces.nsIInterfaceRequestor)
-             .getInterface(Components.interfaces.nsIWebBrowserPrint);
+  gWbp = window.frames[1].document.docShell.printPreview;
   var listener = {
     onLocationChange: function(webProgress, request, location, flags) { },
     onProgressChange: function(webProgress, request, curSelfProgress, 
@@ -61,8 +60,7 @@ function printpreview() {
 }
 
 function exitprintpreview() {
-  window.frames[1].QueryInterface(Components.interfaces.nsIInterfaceRequestor)
-   .getInterface(Components.interfaces.nsIWebBrowserPrint).exitPrintPreview(); 
+  window.frames[1].document.docShell.printPreview.exitPrintPreview();
 }
 
 function finish() {