Add GPU.ANGLE.Buffer11CPUMemoryMB to histograms.xml
Add GPU.ANGLE.Buffer11CPUMemoryMB to histograms.xml

This histograms tracks the sum of CPU memory allocations of Buffer11
copies in order to measure the impact of copy pruning methods.

BUG=angleproject:516

Review URL: https://codereview.chromium.org/1280743003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#342355}

Chilledheart/chromium,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,Pluto-tv/chromium-crosswalk,Pluto-tv/chromium-crosswalk,Pluto-tv/chromium-crosswalk,axinging/chromium-crosswalk,Pluto-tv/chromium-crosswalk,axinging/chromium-crosswalk,Chilledheart/chromium,Just-D/chromium-1,Just-D/chromium-1,Pluto-tv/chromium-crosswalk,Pluto-tv/chromium-crosswalk,Just-D/chromium-1,axinging/chromium-crosswalk,Just-D/chromium-1,Just-D/chromium-1,Just-D/chromium-1,axinging/chromium-crosswalk,axinging/chromium-crosswalk,Just-D/chromium-1,Pluto-tv/chromium-crosswalk,Chilledheart/chromium,Chilledheart/chromium,Pluto-tv/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,Chilledheart/chromium,Chilledheart/chromium,Chilledheart/chromium,axinging/chromium-crosswalk,Just-D/chromium-1,Just-D/chromium-1,Chilledheart/chromium,Pluto-tv/chromium-crosswalk,Chilledheart/chromium