New resolution change policies for desktop and tab capture.
This change replaces the "fixed" versus "variable" resolution change
policies with a 3-tier set: fixed, variable with fixed aspect ratio, and
variable at any aspect ratio.
This allows users of the desktop and tab capture APIs to specify minimum
and maximum resolutions, and from those, a resolution change policy is
determined. The policy is used by the desktop and tab capture
implementation to activate or disable sender-side letterboxing of
screen-capture content.
BUG=473336
NOPRESUBMIT=true
NOTRY=true
Review URL: https://codereview.chromium.org/
1124263004
Cr-Commit-Position: refs/heads/master@{#329056}