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This ability was added for Android WebView to limit the number of
gralloc buffers, which has a low limit on the number of allocations.
Android WebView no longer uses gralloc buffers, so no need to keep this
ability.

Use memory limit to limit the staging resource pool for 1-copy
rasterizer.

BUG=426548

Review URL: https://codereview.chromium.org/643993005

Cr-Commit-Position: refs/heads/master@{#301559}