Implement the texture uploading of ASTC compression for WebGL

This is part I (the Chromium src repo.)

This feature is for ARM and mobile devices.
It's focused the power efficiency benefits
of texture compression, most of which come from reducing
the bandwidth needed for data transfers on the mobile device.

The ASTC compression is involved including reducing memory
footprint and loading time and even increase performance.

This implementation has been verified on the Galaxy S6.
I also plan to apply this feature on the Smart TV.

BUG=516672

Review URL: https://codereview.chromium.org/1263043006

Cr-Commit-Position: refs/heads/master@{#346198}
6 files changed