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There are two icon properties, kAppIcon and kWindowIcon. For the
purposes of Ash, these are used interchangeably (kAppIcon is preferred
and kWindowIcon is a fallback). Thus we can skip sending kWindowIcon.
This should cut down on memory usage by half.

Further, the only place that the icon is used for single process
mash is in overview mode, which displays the icon at 24dip. We can
downscale the icon before sending it over. For tabbed browser windows,
that's 24dip*24dip instead of 192px * 192px.

Since the icons are set on the content window as well as the root
window, they are each copied to the window service twice. We do need
to transport the icons that are set on the root window, but not on
the content window. PropertyConverter doesn't distinguish on the window
type, so new keys are introduced for the root window: kAppIconSmallKey
and kAppIconLargeKey. These are the only ones that are sent to the WS.
They are only used in Mash. kAppIconKey and kWindowIconKey are retained
for use in the browser, e.g. by AppWindowLauncherItemController.
kAppIconLargeKey is only set by the task manager and used by
ShelfWindowWatcher for the shelf icon.

The net effect is that every browser window goes from allocating
192x192px four times, to 24x24dip once. According to chrome://tracing
this lops about 4MiB off malloc'd memory in the browser process when
there are 10 browser windows open.

Bug: 938105

Change-Id: I7bc04784ff3fb1d0857219eae2184542b1f14fd4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1504164Reviewed-by: Michael Wasserman <msw@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Auto-Submit: Evan Stade <estade@chromium.org>
Commit-Queue: Evan Stade <estade@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638622}