Add LibraryMirror.declarations and ClassMirror.declarations to the API and both implementations.

tests/lib/lib.status

Index: tests/lib/lib.status
diff --git a/tests/lib/lib.status b/tests/lib/lib.status
index 67eddd715d3a3976b7dc038cf6de8d0946fb5f3f..4bcba8823869ba6e39b71af7165aa7dade3eb076 100644
--- a/tests/lib/lib.status
+++ b/tests/lib/lib.status
@@ -15,6 +15,7 @@ math/low_test: RuntimeError
 math/random_test: RuntimeError
 
 mirrors/basic_types_in_dart_core_test: RuntimeError # Issue 14025
+mirrors/class_declarations_test/none: RuntimeError # Issue 13440
 mirrors/closures_test/none: RuntimeError # Issue 6490
 mirrors/closure_mirror_find_in_context_test: Fail # Issue 6490
 mirrors/constructor_kinds_test: RuntimeError # Issue 13799
@@ -45,6 +46,7 @@ mirrors/invoke_closurization_test: RuntimeError # Issue 13002
 mirrors/invoke_named_test/none: RuntimeError # Issue 12863
 mirrors/invoke_private_test: CompileTimeError # Issue 12164
 mirrors/invoke_throws_test: RuntimeError # Issue 11954
+mirrors/library_declarations_test/none: RuntimeError # Issue 13439, Issue 13733
 mirrors/library_metadata2_test/01: CompileTimeError # Issue 13633
 mirrors/library_uri_io_test: Skip # Not intended for dart2js as it uses dart:io.
 mirrors/method_mirror_name_test: RuntimeError # Issue 6335