make kPathRefGenIDBitCnt private

kPathRefGenIDBitCnt is used only by SkPath.cpp and SkPathRef.cpp.
Curiously, there's no existing private declarations shared by
SkPath and SkPathRef, so I added kPathRefGenIDBitCnt to
SkPathPriv.h as the go-between. If there's an existing convention
I overlooked, please let me know.

R=reed@google.com,djsollen@google.com
Bug: skia: 6898
Change-Id: I929d780c3b4a10e5cf78e7176a7516abf912508e
Reviewed-on: https://skia-review.googlesource.com/46560
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Commit-Queue: Cary Clark <caryclark@skia.org>
diff --git a/src/core/SkPath.cpp b/src/core/SkPath.cpp
index 5dcca6f..99d7e1a 100644
--- a/src/core/SkPath.cpp
+++ b/src/core/SkPath.cpp
@@ -341,8 +341,8 @@
 uint32_t SkPath::getGenerationID() const {
     uint32_t genID = fPathRef->genID();
 #ifdef SK_BUILD_FOR_ANDROID_FRAMEWORK
-    SkASSERT((unsigned)fFillType < (1 << (32 - kPathRefGenIDBitCnt)));
-    genID |= static_cast<uint32_t>(fFillType) << kPathRefGenIDBitCnt;
+    SkASSERT((unsigned)fFillType < (1 << (32 - SkPathPriv::kPathRefGenIDBitCnt)));
+    genID |= static_cast<uint32_t>(fFillType) << SkPathPriv::kPathRefGenIDBitCnt;
 #endif
     return genID;
 }