Improve prettified-text performance in heap dumps am: c069a1ecc8

Original change: https://android-review.googlesource.com/c/platform/art/+/2484735

Change-Id: I14d606b07f8224c3cc9f88f435b1d15787e84299
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>