Don't cache non-Interceptor interceptors.

Don't cache non-Interceptor interceptors.

R=ngeoffray@google.com

Committed: https://code.google.com/p/dart/source/detail?r=26138

[ahe, 2013-08-14 00:22:28]

Please take a look at these changes.

I'll also write a test before submitting, I need to test something like this:

class Foo {
  Foo(this.length);
  int length;
}

Expect.equals(1, reflect(new Foo(1)).getField(#length).reflectee);
Expect.equals(2, reflect(new Foo(2)).getField(#length).reflectee);
Expect.equals(0, reflect([]).getField(#length).reflectee);

[ngeoffray, 2013-08-14 07:31:12]

LGTM

[ahe, 2013-08-14 19:16:02]

Added test as described. Submitting.

[ahe, 2013-08-14 19:16:46]

Committed patchset #3 manually as r26138 (presubmit successful).