[dart2wasm] Disallow inlining code from main module into dynamic module.

This inlining would require increasing the exported surface area of the main module and would increase the complexity of the contract between modules.

Change-Id: I6d0bc50600b93ea86842cdf136fd7da6e30109bb
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/428202
Reviewed-by: Martin Kustermann <[email protected]>
Commit-Queue: Nate Biggs <[email protected]>

Author: natebiggs

pkg/dart2wasm/lib/translator.dart

@@ -1633,6 +1633,11 @@ class Translator with KernelNodes {
 
   bool shouldInline(Reference target, w.FunctionType signature) {
     if (!options.inlining) return false;
+    if (isDynamicSubmodule && moduleForReference(target) == mainModule) {
+      // We avoid inlining code from the main module into dynamic submodules
+      // so that we can avoid needing to export more code.
+      return false;
+    }
 
     // Unchecked entry point functions perform very little, mainly optional
     // parameter handling and then call the real body function.