Handle UINodes being moved around the Effen tree.

Handle UINodes being moved around the Effen tree.

Changes:
- Remove all the old tracing logic since that was a lot of code for
  just random printf debugging and nobody seems to use it
- Convert "defunct", a permanent state transition, to "mounted", a
  state that can be entered and exitted arbitrarily
- Coallesce mount/unmount notifications so there's only one per frame
- Remove handleRemoved() since we don't use it
- Rename a local variable 'parent' to 'ancestor' to avoid shadowing
  the field
- Replace uses of forEach() with for-in

Effects:
- Reusing a node provided to a constructor in a new place in a tree
  (especially at a different depth) no longer fails (it used to fail
  because the node would be marked defunct then remounted later, at
  which point it would fail)

R=abarth@chromium.org

Committed: https://chromium.googlesource.com/external/mojo/+/1ddf892c641ad2b229752b0b515237e85a354caf

[abarth-chromium, 2015-06-08 16:52:50]

abarth@chromium.org changed reviewers:
+ abarth@chromium.org

[abarth-chromium, 2015-06-08 16:52:51]

lgtm

https://codereview.chromium.org/1169673002/diff/20001/sky/sdk/lib/framework/f...
File sky/sdk/lib/framework/fn2.dart (right):

https://codereview.chromium.org/1169673002/diff/20001/sky/sdk/lib/framework/f...
sky/sdk/lib/framework/fn2.dart:71: _mountedChanged.forEach((UINode node) {
for (UINode node in _mountedChanged) {
}

[Hixie, 2015-06-08 16:59:42]

Committed patchset #2 (id:20001) manually as
1ddf892c641ad2b229752b0b515237e85a354caf (presubmit successful).