Add Gr*Proxy classes

This isn't wired in anywhere yet.

GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1937553002

Committed: https://skia.googlesource.com/skia/+/de5bf0cfeca908b81a28cc50065f7bc2da3d2fd1

Committed: https://skia.googlesource.com/skia/+/92605b35efa0155c44d24bd8415b4cc1db8831db

Review-Url: https://codereview.chromium.org/1937553002
diff --git a/include/core/SkTypes.h b/include/core/SkTypes.h
index f9d0c53..f99bb01 100644
--- a/include/core/SkTypes.h
+++ b/include/core/SkTypes.h
@@ -442,6 +442,15 @@
     kYes = true
 };
 
+/**
+ * Indicates whether a backing store needs to be an exact match or can be larger
+ * than is strictly necessary
+ */
+enum class SkBackingFit {
+    kApprox,
+    kExact
+};
+
 ///////////////////////////////////////////////////////////////////////////////
 
 /** Use to combine multiple bits in a bitmask in a type safe way.