change signature for virtual related to saveLayer, passing SaveLayerRec

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1533953002

NOTREECHECKS=True

Review URL: https://codereview.chromium.org/1533953002
diff --git a/src/core/SkRecorder.cpp b/src/core/SkRecorder.cpp
index c7a826f..67429a6 100644
--- a/src/core/SkRecorder.cpp
+++ b/src/core/SkRecorder.cpp
@@ -336,10 +336,8 @@
     APPEND(Save);
 }
 
-SkCanvas::SaveLayerStrategy SkRecorder::willSaveLayer(const SkRect* bounds,
-                                                      const SkPaint* paint,
-                                                      SkCanvas::SaveFlags flags) {
-    APPEND(SaveLayer, this->copy(bounds), this->copy(paint), flags);
+SkCanvas::SaveLayerStrategy SkRecorder::getSaveLayerStrategy(const SaveLayerRec& rec) {
+    APPEND(SaveLayer, this->copy(rec.fBounds), this->copy(rec.fPaint), rec.fSaveLayerFlags);
     return SkCanvas::kNoLayer_SaveLayerStrategy;
 }