Add a helper function for allocating XPointer ranges.

BUG=624011

Review-Url: https://codereview.chromium.org/2121073002
Cr-Original-Commit-Position: refs/heads/master@{#408330}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 6eee7eee18990d52a5e0723058f0e4d186e1e278
2 files changed