Make GrOp::onPrePrepare be pure virtual

This makes onPrePrepare match onPrepare & onExecute. Most of the new method bodies will-have-to/should be filled in anyway.

Change-Id: Ifc897feaeb2d8fe6eec3ac3a8e91f99393ad6758
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/277542
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
diff --git a/src/gpu/ops/GrDrawableOp.cpp b/src/gpu/ops/GrDrawableOp.cpp
index d50c26b..19291b8 100644
--- a/src/gpu/ops/GrDrawableOp.cpp
+++ b/src/gpu/ops/GrDrawableOp.cpp
@@ -25,7 +25,7 @@
                            const SkRect& bounds)
         : INHERITED(ClassID())
         , fDrawable(std::move(drawable)) {
-        this->setBounds(bounds, HasAABloat::kNo, IsHairline::kNo);
+    this->setBounds(bounds, HasAABloat::kNo, IsHairline::kNo);
 }
 
 void GrDrawableOp::onExecute(GrOpFlushState* state, const SkRect& chainBounds) {