Move sharding functions for reuse

Move shardPaths and shardTests to android.ShardPaths and
android.ShardStrings for reuse in other packages.

Test: m checkbuild
Change-Id: I868802872c73616b80f56cbf11f959c01a8b793a

android/util.go

@@ -319,3 +319,36 @@ func SplitFileExt(name string) (string, string, string) {
 
 	return root, suffix, ext
 }
+
+// ShardPaths takes a Paths, and returns a slice of Paths where each one has at most shardSize paths.
+func ShardPaths(paths Paths, shardSize int) []Paths {
+	if len(paths) == 0 {
+		return nil
+	}
+	ret := make([]Paths, 0, (len(paths)+shardSize-1)/shardSize)
+	for len(paths) > shardSize {
+		ret = append(ret, paths[0:shardSize])
+		paths = paths[shardSize:]
+	}
+	if len(paths) > 0 {
+		ret = append(ret, paths)
+	}
+	return ret
+}
+
+// ShardStrings takes a slice of strings, and returns a slice of slices of strings where each one has at most shardSize
+// elements.
+func ShardStrings(s []string, shardSize int) [][]string {
+	if len(s) == 0 {
+		return nil
+	}
+	ret := make([][]string, 0, (len(s)+shardSize-1)/shardSize)
+	for len(s) > shardSize {
+		ret = append(ret, s[0:shardSize])
+		s = s[shardSize:]
+	}
+	if len(s) > 0 {
+		ret = append(ret, s)
+	}
+	return ret
+}