Extract RenderLayer::physicalBoundingBoxIncludingReflectionAndStackingChildren

Three of the callers of RenderLayer::calculateLayerBounds want this function to
do something quite different from what the other callers want. These three
callers are part of the paint phase and are trying to compute the input rect
for software filters.

Prior to this CL, these three callers passed 0 for the flags argument to
RenderLayer::calculateLayerBounds. After this CL, these callers instead call
physicalBoundingBoxIncludingReflectionAndStackingChildren, which contains just
the parts of calculateLayerBounds that they actually want to use. Now, all the
callers to calculateLayerBounds pass in the default flags, which opens the door
to simplifying calculateLayerBounds.

Review URL: https://codereview.chromium.org/225423005

git-svn-id: svn://svn.chromium.org/blink/trunk@170916 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Add ExcludeHiddenDescendants to DefaultCalculateLayerBoundsFlags

All the callers that pass the DefaultCalculateLayerBoundsFlags to
RenderLayer::calculateLayerBounds actually want to ExcludeHiddenDescendants.

Review URL: https://codereview.chromium.org/224843006

git-svn-id: svn://svn.chromium.org/blink/trunk@170917 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Actually send the compositing reasons in the debug info

Looks like some plumbing got missed in a refactor.

BUG=None

Review URL: https://codereview.chromium.org/226833002

git-svn-id: svn://svn.chromium.org/blink/trunk@170918 bbb929c8-8fbe-4397-9dbb-9b2b20218538