+tedchoc@ to keep me honest here.

I think the toolbar is special in that it is our core UI and is shown frequently. The ToolbarViewResourceAdapter is used to draw the C++ compositor version of the toolbar and is needed frequently (e.g. when the toolbar scrolls on or offscreen).

Indeed.  We should just see what happens in the case where we drop it.  If we could force simulate memory pressure easily, it would be cool to get a video of it dropping while scrolling off or just before we start the scroll.

It is definitely one of the last things I think we should drop, but if it prevents the page from being killed, having the omnibox flicker one frame seems like an OK compromise.

We can simulate memory pressure via adb:
adb shell am send-trim-memory com.android.chrome RUNNING_CRITICAL

I tested with my prototype a bit and didn't see any jank when scrolling on the page or side-swiping. I've uploaded the CL at https://chromium-review.googlesource.com/c/577869/ if anyone wants to take a look.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a1c8ef36d3468f1369efb2bbc81ec39018edba31

commit a1c8ef36d3468f1369efb2bbc81ec39018edba31
Author: Bernhard Bauer <bauerb@chromium.org>
Date: Mon Oct 16 19:12:24 2017

Drop ToolbarViewResourceAdapter bitmap under memory pressure.

To force a memory pressure signal for testing, run this command:
$ adb shell am send-trim-memory <package> RUNNING_CRITICAL

Bug:  746472 
Change-Id: Ib3d74f7de537ae8ae0f2c04f4228e53a9747349b
Reviewed-on: https://chromium-review.googlesource.com/577869
Commit-Queue: Bernhard Bauer <bauerb@chromium.org>
Reviewed-by: Ted Choc <tedchoc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#509129}
[modify] https://crrev.com/a1c8ef36d3468f1369efb2bbc81ec39018edba31/chrome/android/java/src/org/chromium/chrome/browser/ChromeActivity.java
[modify] https://crrev.com/a1c8ef36d3468f1369efb2bbc81ec39018edba31/ui/android/java/src/org/chromium/ui/resources/dynamics/ViewResourceAdapter.java