[flow analysis] Update rebasePromotedTypes to match spec.

The following changes are made to `rebasePromotedTypes`, to make it
more accurately reflect the specification changes in
https://github.com/dart-lang/language/pull/4427.

- The order of arguments is reversed to match the order of arguments
  in the spec.

- The arguments are renamed to match the argument names in the spec,
  and they are changed into named arguments so that the call sites are
  clearer.

- Comments are updated to reflect which parts of the algorithm come
  from the spec and which parts are optimizations.

There is no functional change.

Change-Id: I0d45654ad14a6414bc1cba7c56cfc66b561c7441
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/443462
Commit-Queue: Paul Berry <paulberry@google.com>
Reviewed-by: Erik Ernst <eernst@google.com>

https://dart.googlesource.com/sdk/+/9248bba5cb66e3003406ef93ad94e95f80575737

DEPS

diff --git a/DEPS b/DEPS
index f2f839a..38de1f3 100644
--- a/DEPS
+++ b/DEPS
@@ -229,7 +229,7 @@
 ]
 
 deps = {
-  'flutter/engine/src/flutter/third_party/dart': Var('dart_git') + '/sdk' + '@' + '21a9b007029e0067df9e29d83b03389c468145b0',
+  'flutter/engine/src/flutter/third_party/dart': Var('dart_git') + '/sdk' + '@' + '9248bba5cb66e3003406ef93ad94e95f80575737',
 
   'flutter': Var('flutter_git') + '/mirrors/flutter' + '@' + '8047f8a01ee0f0496b79e1198d0062eea3560989',
 

commits.json

diff --git a/commits.json b/commits.json
index 4a1ea29..2552d9f 100644
--- a/commits.json
+++ b/commits.json
@@ -1,4 +1,4 @@
 {
   "flutter":"8047f8a01ee0f0496b79e1198d0062eea3560989",
-  "flutter/engine/src/flutter/third_party/dart":"21a9b007029e0067df9e29d83b03389c468145b0"
+  "flutter/engine/src/flutter/third_party/dart":"9248bba5cb66e3003406ef93ad94e95f80575737"
 }
\ No newline at end of file