Introduce a flag to disable string operator +

Introduce a flag to disable string operator +

If allow_string_plus is set to false, the compiler will report an error
when it finds a string literal followed by +. Invoking the + operator on a
string value throws a noSuchMethod exception.

This is temporary code that we'll eliminate once the + operator on
strings is completely removed.
Committed: https://code.google.com/p/dart/source/detail?r=6423

[Ivan Posva, 2012-04-11 12:03:56]

LGTM -ip

https://chromiumcodereview.appspot.com/9960084/diff/1/runtime/lib/string.cc
File runtime/lib/string.cc (right):

https://chromiumcodereview.appspot.com/9960084/diff/1/runtime/lib/string.cc#n...
runtime/lib/string.cc:121: DECLARE_FLAG(bool, allow_string_plus);
Usually we try to declare flags at the top of the file, but since this is
temporary I do like it better here as well.

[srdjan, 2012-04-11 18:32:03]

DBC

https://chromiumcodereview.appspot.com/9960084/diff/5001/runtime/lib/string.dart
File runtime/lib/string.dart (right):

https://chromiumcodereview.appspot.com/9960084/diff/5001/runtime/lib/string.d...
runtime/lib/string.dart:238: String plus(String other) native "String_plus";
Why not making it private (_plus)?

[hausner, 2012-04-11 18:36:22]

https://chromiumcodereview.appspot.com/9960084/diff/5001/runtime/lib/string.dart
File runtime/lib/string.dart (right):

https://chromiumcodereview.appspot.com/9960084/diff/5001/runtime/lib/string.d...
runtime/lib/string.dart:238: String plus(String other) native "String_plus";
On 2012/04/11 18:32:03, srdjan wrote:
> Why not making it private (_plus)?

Yes, would have been a good idea. But this code goes away in short time, so I
would not worry about it. Also, it's not exposed through the interface.