Previously annotations added between saveLayer/restore were lost.
Merge annotations in SkPDFDevice::drawDevice(). Also modified code to
apply correct transformation and clipping on annotations added between
saveLayer/restore:
- Apply the initial transform only when adding the annotations into the
doc, otherwise we need to unapply sub-device's initial transform
before merging the annotations into parent-device.
- Apply only device-local clipping. fClipStack is in global coordinates,
which is not suitable to clip rects in sub-devices.
BUG=skia:4080
BUG=503515
Review URL: https://codereview.chromium.org/1257533004
