Bug 1540015 - part 3: Rename Document::GetShell() to Document::GetPresShell() and make it return PresShell* rather than nsIPresShell* r=smaug,emilio

This makes `Document::GetShell()` return `PresShell*` instead of `nsIPresShell`.

Additonally, "shell" is unclear ("docshell" vs. "presshell").  Therefore, this
also renames `Document::GetShell()` to `Document::GetPresShell()`.

Similarly, some other method names of `Document` are also renamed from
`*Shell*` to `*PresShell*`.

Differential Revision: https://phabricator.services.mozilla.com/D25338

dom/html/ImageDocument.cpp

@@ -12,6 +12,7 @@
 #include "mozilla/dom/ImageDocumentBinding.h"
 #include "mozilla/dom/HTMLImageElement.h"
 #include "mozilla/dom/MouseEvent.h"
+#include "mozilla/PresShell.h"
 #include "mozilla/StaticPrefs.h"
 #include "nsRect.h"
 #include "nsIImageLoadingContent.h"
@@ -26,7 +27,6 @@
 #include "imgILoader.h"
 #include "imgIContainer.h"
 #include "imgINotificationObserver.h"
-#include "nsIPresShell.h"
 #include "nsPresContext.h"
 #include "nsIChannel.h"
 #include "nsIContentPolicy.h"
@@ -402,12 +402,12 @@ void ImageDocument::ScrollImageTo(int32_t aX, int32_t aY, bool restoreImage) {
     FlushPendingNotifications(FlushType::Layout);
   }
 
-  nsCOMPtr<nsIPresShell> shell = GetShell();
-  if (!shell) {
+  RefPtr<PresShell> presShell = GetPresShell();
+  if (!presShell) {
     return;
   }
 
-  nsIScrollableFrame* sf = shell->GetRootScrollFrameAsScrollable();
+  nsIScrollableFrame* sf = presShell->GetRootScrollFrameAsScrollable();
   if (!sf) {
     return;
   }
@@ -835,9 +835,9 @@ float ImageDocument::GetZoomLevel() {
 #if defined(MOZ_WIDGET_ANDROID)
 float ImageDocument::GetResolution() {
   float resolution = mOriginalResolution;
-  nsCOMPtr<nsIPresShell> shell = GetShell();
-  if (shell) {
-    resolution = shell->GetResolution();
+  RefPtr<PresShell> presShell = GetPresShell();
+  if (presShell) {
+    resolution = presShell->GetResolution();
   }
   return resolution;
 }