try to forward toString() on js before calling Dart toString()
replace Constructor with Serializable<FunctionProxy> to be more flexible
fix jmesserly comments
Merge pull request #69 from a14n/remove-constructor

replace Constructor with Serializable<FunctionProxy>
Merge pull request #61 from a14n/issue-61

Can't call JavaScript toString() method using js.Proxy object
Clean up JS interop samples.

Clean up these samples to simplify presentation.  I did this a part of a recent talk.

TBR=alexandre.ardhuin@gmail.com,

Review URL: https://chromiumcodereview.appspot.com//13902016
Fixes for M4
Update version
Merge branch 'master' into fix-list-changes
update for M4