Fix performance regression from Blink r154194.

Change in Blink r154194 caused perf regression on tests that use many floating
objects.

This change reduces the overhead of clearFloats(), at the cost of leaving
obsolete container references in the floating object container map. These
references are cleared when the float or the containing RenderBlock is
deleted. In most cases when these references are being removed, they will be
re-added again during layout anyway.

BUG=260286
R=inferno@chromium.org

Review URL: https://chromiumcodereview.appspot.com/19240005

git-svn-id: svn://svn.chromium.org/blink/trunk@154327 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Revert "Reland change to enable deferred image decoding for animated GIFs" and rebaselines.

This reverts commit f270364ec689a471b2fb1307a006158d260eb45b and dcd6f7493c64721bc003a382ca0e2931b00de8fc.

Conflicts:
	LayoutTests/platform/win-xp/virtual/deferred/fast/images/webp-color-profile-lossy-expected.png

BUG=169377,259783
TBR=hclam,ojan

Review URL: https://codereview.chromium.org/19422003

git-svn-id: svn://svn.chromium.org/blink/trunk@154328 bbb929c8-8fbe-4397-9dbb-9b2b20218538