Make it harder to forget itemCount for FixedHeightScrollable

Make it harder to forget itemCount for FixedHeightScrollable

Previously, if a subclass of FixedHeightScrollable didn't set itemCount,
everything would silently work except that you wouldn't actully be able to
scroll. This CL makes it harder to forget to provide the itemCount by making it
an abstract getter. Now the analyzer will flag it as missing in subclasses and
we'll throw an exception at runtime if you forget it.

R=ianh@google.com, tonyg@google.com

Committed: https://chromium.googlesource.com/external/mojo/+/e14757d2a9aeed883e1e33878fe4cba9ee9dbbee

[Hixie, 2015-07-07 15:25:13]

ianh@google.com changed reviewers:
+ ianh@google.com

[Hixie, 2015-07-07 15:25:13]

lgtm

https://codereview.chromium.org/1219933004/diff/1/sky/sdk/example/stocks/lib/...
File sky/sdk/example/stocks/lib/stock_list.dart (right):

https://codereview.chromium.org/1219933004/diff/1/sky/sdk/example/stocks/lib/...
sky/sdk/example/stocks/lib/stock_list.dart:16: this.query
do we still need to remember the query?

[abarth-chromium, 2015-07-07 15:26:21]

https://codereview.chromium.org/1219933004/diff/1/sky/sdk/example/stocks/lib/...
File sky/sdk/example/stocks/lib/stock_list.dart (right):

https://codereview.chromium.org/1219933004/diff/1/sky/sdk/example/stocks/lib/...
sky/sdk/example/stocks/lib/stock_list.dart:16: this.query
On 2015/07/07 at 15:25:13, Hixie wrote:
> do we still need to remember the query?

Nope!

[Hixie, 2015-07-07 15:27:36]

we should probably hoist the filtering up to the list owner, so we don't
refilter on construction. We should probably establish a rule that Widget
constructors must be fast.

[abarth-chromium, 2015-07-07 15:43:46]

On 2015/07/07 at 15:27:36, ianh wrote:
> we should probably hoist the filtering up to the list owner, so we don't
refilter on construction. We should probably establish a rule that Widget
constructors must be fast.

Done.

[abarth-chromium, 2015-07-07 15:44:32]

Committed patchset #2 (id:20001) manually as
e14757d2a9aeed883e1e33878fe4cba9ee9dbbee (presubmit successful).

[tonyg, 2015-07-07 15:58:03]

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

[tonyg, 2015-07-07 15:58:04]

lgtm

Thanks

[Hixie, 2015-07-07 16:00:03]

lgtm