SkVarAlloc::approxBytesAllocated()

This is what I was getting at on the other CL.

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/f27f1bcce50c8f95aea8469684a70b70c9baee09

CQ_EXTRA_TRYBOTS=client.skia.android:Test-Android-Nexus5-Adreno330-Arm7-Release-Trybot

Review URL: https://codereview.chromium.org/730193003
4 files changed