optimize usage of observers in MDV and PolymerExpressions

[jmesserly]

We often create observers even for silly things, e.g. observing the "value" property of a CompoundBindings. FancySyntax has even more observers. We can skip at least the PathObserver if the thing we're observing just has a ".value"

[sethladd]

Still an issue?

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Removed Library-FancySyntax label.
Added Library-PolymerExpressions label.
Changed the title to: "optimize usage of observers in MDV and PolymerExpressions".

[justinfagnani]

Yes

[sigmundch]

Added this to the M8 milestone.

[sigmundch]

Removed this from the M8 milestone.
Added this to the Later milestone.

[jmesserly]

this is partially fixed. NodeBinding is smart about not creating yet-another-pathobserer. TemplateIterator is smarter too.

Still work to be done:

• PolymerExpressions is creating way too many Scopes.
• we still create PathObservers for empty paths.
• need another special case for "value" in PathObserver. would be nice to avoid dart:mirrors.
• also need a special case for a single-segment path.

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Removed Library-MDV label.

[sigmundch]

Removed this from the Later milestone.
Added this to the M9 milestone.

[clayberg]

Removed this from the M9 milestone.
Added this to the 1.1 milestone.

[sigmundch]

Removed this from the 1.1 milestone.
Added this to the 1.2 milestone.

[anders-sandholm]

Removed Library-Observe label.
Added Pkg-Observe label.

[jmesserly]

Rafael has been slowly fixing this on the observe-js/TemplateBinding/polymer-expressions side of the world, and we've been porting those changes. I'd say it's good enough at this point.

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Added Fixed label.