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>

bench/ImageCycleBench.cpp

@@ -73,7 +73,9 @@ protected:
                 }
             }
             // Prevent any batching between "frames".
-            canvas->flush();
+            if (auto surf = canvas->getSurface()) {
+                surf->flush();
+            }
         }
     }
 

include/core/SkCanvas.h

@@ -286,6 +286,11 @@ public:
     */
     virtual GrContext* getGrContext();
 
+    /** Sometimes a canvas is owned by a surface. If it is, getSurface() will return a bare
+     *  pointer to that surface, else this will return nullptr.
+     */
+    SkSurface* getSurface() const;
+
     /** Returns the pixel base address, SkImageInfo, rowBytes, and origin if the pixels
         can be read directly. The returned address is only valid
         while SkCanvas is in scope and unchanged. Any SkCanvas call or SkSurface call

src/core/SkCanvas.cpp

@@ -619,6 +619,10 @@ void SkCanvas::onFlush() {
     }
 }
 
+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);