Add frame/root element accessor helpers to SVGImage

This abstracts away most of the accesses to the Page object, reducing
the amount of boilerplate a bit. It'll also make it easier to transition
away from the current Page/Document setup to allow sharing some code
with SVG resource documents.

Also add a LayoutRoot() for additional simplification.

Bug: 109212
Change-Id: I7db0e29cbe28cc31c1f1df0546a3266abf6141e3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2544970Reviewed-by: Stephen Chenney <schenney@chromium.org>
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#829157}

third_party/blink/renderer/core/svg/graphics/svg_image.h

@@ -41,10 +41,13 @@
 namespace blink {
 
 class Document;
+class LayoutSVGRoot;
+class LocalFrame;
 class Page;
 class PaintController;
 class SVGImageChromeClient;
 class SVGImageForContainer;
+class SVGSVGElement;
 struct IntrinsicSizingInfo;
 
 // SVGImage does not use Skia to draw images (as BitmapImage does) but instead
@@ -203,6 +206,10 @@ class CORE_EXPORT SVGImage final : public Image {
   void LoadCompleted();
   void NotifyAsyncLoadCompleted();
 
+  LocalFrame* GetFrame() const;
+  SVGSVGElement* RootElement() const;
+  LayoutSVGRoot* LayoutRoot() const;
+
   class SVGImageLocalFrameClient;
 
   Persistent<SVGImageChromeClient> chrome_client_;