Remove one more use of mirrors: Components now have to explicitly sync their fields.

Remove one more use of mirrors: Components now have to explicitly sync their fields.

This also removes one bit of magic to make it more obvious what on is
going on during a sync, which should hopefully help.

Components have to decide if they support being stateful or not. If
they do, then they must implement syncFields() and have mutable
fields; if they don't, then they must have final fields. This isn't
particularly enforced, though.

This also renames _willSync() to _retainStatefulNodeIfPossible(), for
clarity, and fixes some minor style issues and one typo that was
breaking the drawer.

R=abarth@chromium.org

Committed: https://chromium.googlesource.com/external/mojo/+/3bacbb2f7b295147c4201c66868805e954b2dbb7

[abarth-chromium, 2015-06-10 17:07:57]

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

[abarth-chromium, 2015-06-10 17:07:58]

lgtm

https://codereview.chromium.org/1174023003/diff/20001/sky/sdk/lib/framework/c...
File sky/sdk/lib/framework/components2/fixed_height_scrollable.dart (right):

https://codereview.chromium.org/1174023003/diff/20001/sky/sdk/lib/framework/c...
sky/sdk/lib/framework/components2/fixed_height_scrollable.dart:46: var
itemNumber = 0;
s/itemNumber/itemShowNumber/

[Hixie, 2015-06-10 17:33:09]

Committed patchset #4 (id:60001) manually as
3bacbb2f7b295147c4201c66868805e954b2dbb7 (presubmit successful).