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This patch uses glClear to draw the solid color draw quad whenever
possible. It also replaces the usage of color transform matrix used
in the fragment shader for solid color draw quad with a precomputed
color that is in the correct color space.

Improves draw time of a full screen solid color quad by approximately
80% on Atlas. (From ~1.5ms to about ~0.25ms)

Also adds a feature flag that is disabled by default and will be enabled
in subsequent CLs. (For easy revert of feature)

Bug: 1072895,1072910
Test: Manually tested on Chrome OS
Change-Id: I0d0174bffa802d146bce26f985bc3150e051dc05
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2343970
Commit-Queue: Malay Keshav <malaykeshav@chromium.org>
Reviewed-by: Daniele Castagna <dcastagna@chromium.org>
Cr-Commit-Position: refs/heads/master@{#813018}