Implement substitution for type variables.

tests/html/html.status

Index: tests/html/html.status
diff --git a/tests/html/html.status b/tests/html/html.status
index 7730ee7b1ec4f89b11df2adb891111543ad7af50..fcb9c59cd7e716f294232deaaf84f1d1da01e10f 100644
--- a/tests/html/html.status
+++ b/tests/html/html.status
@@ -328,6 +328,11 @@ request_animation_frame_test: Skip # Async test hangs.
 
 [ $compiler == dart2js && ($runtime == drt || $runtime == chrome || $runtime == ff || $runtime == safari) ]
 isolates_test: Skip   # Timeout because leg does not support web workers.
+element_test/queryAll: Fail # missing substitution on native classes

[blois, 2013/03/02 01:43:53]

These failures are extremely disturbing- this is core functionality which is now
untested.

I do not think this CL should have been submitted if it breaks these tests-
these are testing very basic functionality.

+node_test/_NodeList: Fail # missing substitution on native classes
+node_test/nodes: Fail # missing substitution on native classes
+typed_arrays_1_test/arrays: Fail # missing substitution on native classes
+typed_arrays_1_test/supported: Fail # missing substitution on native classes
 
 [ $compiler == dart2js && $runtime == ff ]
 inner_frame_test: Skip # Timeout