cc: Make property trees support resourceless draw mode
Property trees currently rely on render target information
computed at tree-building time (on the main thread) when
computing draw properties. However, in resourceless draw
mode (used by Android WebView), only the root render surface
is used. Since resourceless draw mode can be arbitrarily
enabled and disabled on the compositor thread, we cannot
know at tree building time whether it will be used. This
CL makes property trees support resourceless draw mode
without requiring trees to be rebuilt when the draw mode
changes (though they do still need to be updated).
Most of the changes are for computing clipping-related
properties, since render surfaces change the way clips are
propagated to descendants and also change the space in
which drawable_content_rect and clip_rect are expressed.