[CFE] Rename additionalDills to additionalDillModules; don't use it to load platform

* Rename additionalDills to additionalDillModules to indicate that it
   is used to load a "module", not any old dill file.
 * Where additionalDills was used to provide the platform use sdkSummary
   instead.
 * Remove unused constructor in KernelCompilationResults.

Tested: Existing tests.
Change-Id: I5f73f61db73b2bc932c211fb0b2e66ec2f5c50c5
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/495981
Reviewed-by: Alexander Markov <alexmarkov@google.com>
Reviewed-by: Nicholas Shahan <nshahan@google.com>
Commit-Queue: Jens Johansen <jensj@google.com>
Reviewed-by: Johnni Winther <johnniwinther@google.com>

pkg/dart2bytecode/lib/dart2bytecode.dart

@@ -253,9 +253,9 @@ Future<int> runCompilerWithOptions({
 
   final platformKernelUri = Uri.base.resolveUri(new Uri.file(platformKernel));
 
-  final List<Uri> additionalDills = <Uri>[];
+  final List<Uri> additionalDillModules = <Uri>[];
   if (importDill != null) {
-    additionalDills.add(Uri.base.resolveUri(new Uri.file(importDill)));
+    additionalDillModules.add(Uri.base.resolveUri(new Uri.file(importDill)));
   }
 
   final Uri? dynamicInterfaceSpecificationUri =
@@ -279,7 +279,7 @@ Future<int> runCompilerWithOptions({
   final CompilerOptions compilerOptions = CompilerOptions()
     ..sdkSummary = platformKernelUri
     ..fileSystem = fileSystem
-    ..additionalDills = additionalDills
+    ..additionalDillModules = additionalDillModules
     ..packagesFileUri = packagesUri
     ..dynamicInterfaceSpecificationUri = dynamicInterfaceSpecificationUri
     ..explicitExperimentalFlags = parseExperimentalFlags(

pkg/dart2bytecode/test/bytecode_generator_test.dart

@@ -94,7 +94,7 @@ Future<CompilerResult> compileTestCaseToKernelProgram(
   final options = CompilerOptions()
     ..target = target
     ..omitPlatform = true
-    ..additionalDills = <Uri>[platformKernel]
+    ..sdkSummary = platformKernel
     ..environmentDefines = {}
     ..onDiagnostic = (CfeDiagnosticMessage message) {
       fail("Compilation error: ${message.plainTextFormatted.join('\n')}");