Expose the owning surface to a canvas?

Handy if you want to flush, or otherwise understand the underlying buffer(s).

Change-Id: I3d6610695c8603232192b26c687c6c74512165dd
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/254803
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
diff --git a/src/core/SkCanvas.cpp b/src/core/SkCanvas.cpp
index 72fe22d..9dd0f16 100644
--- a/src/core/SkCanvas.cpp
+++ b/src/core/SkCanvas.cpp
@@ -619,6 +619,10 @@
     }
 }
 
+SkSurface* SkCanvas::getSurface() const {
+    return fSurfaceBase;
+}
+
 SkISize SkCanvas::getBaseLayerSize() const {
     SkBaseDevice* d = this->getDevice();
     return d ? SkISize::Make(d->width(), d->height()) : SkISize::Make(0, 0);