Merge empty path ref bounds initialization into M39.

Merging this CL:
https://skia.googlesource.com/skia/+/51936a3f07d18654be966527691067729c070bd3

Original review:
https://codereview.chromium.org/603503003

Review URL: https://codereview.chromium.org/618753002
diff --git a/src/core/SkPathRef.cpp b/src/core/SkPathRef.cpp
index 64f6fb8..5707693 100644
--- a/src/core/SkPathRef.cpp
+++ b/src/core/SkPathRef.cpp
@@ -30,7 +30,9 @@
 //////////////////////////////////////////////////////////////////////////////
 
 SkPathRef* SkPathRef::CreateEmptyImpl() {
-    return SkNEW(SkPathRef);
+    SkPathRef* empty = SkNEW(SkPathRef);
+    empty->computeBounds();   // Avoids races later to be the first to do this.
+    return empty;
 }
 
 SkPathRef* SkPathRef::CreateEmpty() {