Implement operator call() in dartc

[DartBot]

This issue was originally filed by zundel@google.com

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New in 0.7 rev of the spec, the call operator allows your object to be invoked as if it were a function and the logic defined in the body of the operator is invoked.

// simple test with no types in signature
class A1 {
  operator call() => 42;
}

var a1 = new A1();
Expect.equals(42, a1());

[DartBot]

This comment was originally written by zundel@google.com

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Set owner to zundel@google.com.

[DartBot]

This comment was originally written by zundel@google.com

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Removed the owner.

[kasperl]

Removed Area-Compiler label.
Added Area-Analyzer label.

[sethladd]

Marked this as blocking #2931.

[bwilkerson]

Added this to the M1 milestone.
Removed Priority-Medium label.
Added Priority-Low label.

[anders-sandholm]

Marked this as being blocked by #2931.

[gbracha]

Bear in mind that it is no longer an operator, just a magic method. See recent specs.

[scheglov]

Set owner to @scheglov.
Added Accepted label.

[scheglov]

https://chromiumcodereview.appspot.com/10582003

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Added Started label.

[scheglov]

https://code.google.com/p/dart/source/detail?r=8826

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Added Fixed label.