Add SkiaCanvas::captureCanvasState()

Test: Verified bug is fixed.  Wrote unit test.

Bug: 37268771

Change-Id: I9deb7db353cd2129ad245e7f65419670463bb717
diff --git a/libs/hwui/SkiaCanvas.h b/libs/hwui/SkiaCanvas.h
index 45924f6..af2c23e 100644
--- a/libs/hwui/SkiaCanvas.h
+++ b/libs/hwui/SkiaCanvas.h
@@ -102,6 +102,8 @@
     virtual SkDrawFilter* getDrawFilter() override;
     virtual void setDrawFilter(SkDrawFilter* drawFilter) override;
 
+    virtual SkCanvasState* captureCanvasState() const override;
+
     virtual void drawColor(int color, SkBlendMode mode) override;
     virtual void drawPaint(const SkPaint& paint) override;