Do FinishAllRendering in WM_WINDOWPOSCHANGING

This ensures that the last swap completes before the window is resized, so that the window contents aren't scaled.

BUG=363704

Review URL: https://codereview.chromium.org/277053003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@270206 0039d316-1c4b-4281-b951-d872f2087c98
6 files changed