Paint tab-loading throbbers into a ui::Layer.
In views browsers, updating the tab loading throbber currently requires
a repaint that starts at the BrowserView and trickles the damage
rectangle down until it reaches the favicon area. This uses a lot of CPU
and energy: about 11 watts above idle on a MacBook Pro (and significant
CPU on Linux) for a single "waiting" spinner.
Giving the throbber a layer allows the repaint to be isolated, with
compositing done on the GPU. This brings total energy usage down to
about 2.5 watts above idle.
Plots at http://crbug.com/391646#c44
BUG=391646
TEST=Spinners should look and behave the same, but use less energy/CPU.
Review URL: https://codereview.chromium.org/1393193002
Cr-Commit-Position: refs/heads/master@{#355514}
6 files changed
