Revert "[dart2js] Run static interop erasure regardless if from dill or src"

This reverts commit 5d7029e.

Reason for revert: Increases memory usage in dart2js benchmarks

Original change's description:
> [dart2js] Run static interop erasure regardless if from dill or src
>
> Removes modular transformation as well.
>
> Change-Id: Ib3aafcaf35b72fdb6a93db682dcf8df84842578f
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/266803
> Reviewed-by: Joshua Litt <joshualitt@google.com>
> Commit-Queue: Srujan Gaddam <srujzs@google.com>

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: I8c40f16983a3f7e2383dcf3b47c2134c9ecd6746
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/267762
Reviewed-by: Srujan Gaddam <srujzs@google.com>
Commit-Queue: Srujan Gaddam <srujzs@google.com>
Reviewed-by: Joshua Litt <joshualitt@google.com>

Author: srujzs

pkg/compiler/lib/src/kernel/dart2js_target.dart

@@ -13,6 +13,7 @@ import 'package:_fe_analyzer_shared/src/messages/codes.dart'
 import 'package:_js_interop_checks/js_interop_checks.dart';
 import 'package:_js_interop_checks/src/transformations/export_creator.dart';
 import 'package:_js_interop_checks/src/transformations/js_util_optimizer.dart';
+import 'package:_js_interop_checks/src/transformations/static_interop_class_eraser.dart';
 import 'package:kernel/ast.dart' as ir;
 import 'package:kernel/class_hierarchy.dart';
 import 'package:kernel/core_types.dart';
@@ -168,10 +169,17 @@ class Dart2jsTarget extends Target {
       // in the single pass in `transformations/lowering.dart`.
       jsUtilOptimizer.visitLibrary(library);
     }
+    var staticInteropClassEraser =
+        StaticInteropClassEraser(coreTypes, referenceFromIndex);
     lowering.transformLibraries(libraries, coreTypes, hierarchy, options);
     logger?.call("Lowering transformations performed");
     if (canPerformGlobalTransforms) {
       transformMixins.transformLibraries(libraries);
+      // Do the erasure after any possible mock creation to avoid erasing types
+      // that need to be used during mock conformance checking.
+      for (var library in libraries) {
+        staticInteropClassEraser.visitLibrary(library);
+      }
       logger?.call("Mixin transformations performed");
     }
   }

pkg/compiler/lib/src/phase/load_kernel.dart

@@ -133,16 +133,10 @@ class _LoadFromKernelResult {
 
 void _doGlobalTransforms(Component component) {
   transformMixins.transformLibraries(component.libraries);
-}
-
-// Perform any backend-specific transforms here that can be done on both
-// serialized components and components from source.
-// TODO(srujzs): Can we combine this with the above?
-void _doTransformsOnKernelLoad(Component component) {
-  // referenceFromIndex is only necessary in the case where a module
-  // containing a stub definition is invalidated, and then reloaded, because
-  // we need to keep existing references to that stub valid. Here, we have the
-  // whole program, and therefore do not need it.
+  // referenceFromIndex is only necessary in the case where a module containing
+  // a stub definition is invalidated, and then reloaded, because we need to
+  // keep existing references to that stub valid. Here, we have the whole
+  // program, and therefore do not need it.
   StaticInteropClassEraser(ir.CoreTypes(component), null)
       .visitComponent(component);
 }
@@ -403,9 +397,6 @@ Future<Output?> run(Input input) async {
     moduleLibraries = result.moduleLibraries;
   }
   if (component == null) return null;
-  // TODO(srujzs): These transforms can occur multiple times on the same
-  // component. Currently, it isn't an issue.
-  _doTransformsOnKernelLoad(component);
   if (input.forceSerialization) {
     // TODO(johnniwinther): Remove this when #34942 is fixed.
     List<int> data = serializeComponent(component);