Invalidate subsequence caching & empty paint phases if clips changed.

Invalidate subsequence caching & empty paint phases if clips changed.

Subsequence caching & empty paint phase optimizations need to be invalidated i
any ancestor clips updated, since those clips are used to:

a. Adjust painted output (SPInvalidation only, not SPv2), and
b. Cull out invisible content (SPInvalidation and SPv2)

Previously, we detected that by computing clip rects during paint. This CL
moves it to the pre-paint tree walk.

The CL does not yet work for SPv2, because it does not include computation of
the enclosing transformed ancestor, which will be the SPv2 analogue of
paintInvalidationContainer.

BUG=683733
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

patch from issue 2654643002 at patchset 120001 (http://crrev.com/2654643002#ps120001)