[dartdevc] fix import/export declarations for es6 to add extension

d8 assumes a '.js' extension - e.g.,:
```
import { core, dart, dartx } from 'dart_sdk.js';
```

Note: this will enable Siggi's modular compilation framework to run DDC tests on d8.

Change-Id: I1167a36e1454950149fecb8abc793728a16e4591
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/103780
Reviewed-by: Nicholas Shahan <[email protected]>
Commit-Queue: Vijay Menon <[email protected]>

Author: vsmenon

pkg/dev_compiler/lib/src/js_ast/printer.dart

@@ -1306,7 +1306,7 @@ class Printer implements NodeVisitor {
     if (from != null) {
       out(' from');
       spaceOut();
-      visit(from);
+      out("'${from.valueWithoutQuotes}.js'");
     }
   }
 

pkg/dev_compiler/test/sourcemap/ddc_common.dart

@@ -167,7 +167,7 @@ void createHtmlWrapper(File sdkJsFile, Uri outputFile, String jsContent,
   var sdkFile = File(path.relative(sdkJsFile.path, from: sdkRoot.path));
   String jsRootDart = "/root_dart/${sdkFile.uri}";
   File.fromUri(outputFile.resolve("$outputFilename.html.js")).writeAsStringSync(
-      jsContent.replaceFirst("from 'dart_sdk'", "from '$jsRootDart'"));
+      jsContent.replaceFirst("from 'dart_sdk.js'", "from '$jsRootDart'"));
   File.fromUri(outputFile.resolve("$outputFilename.html.html"))
       .writeAsStringSync(getWrapperHtmlContent(
           jsRootDart, "/root_build/$outputFilename.html.js"));

pkg/dev_compiler/test/sourcemap/sourcemaps_ddc_suite.dart

@@ -70,7 +70,7 @@ class DevCompilerRunner implements CompilerRunner {
 
     var jsContent = File.fromUri(outputFile).readAsStringSync();
     File.fromUri(outputFile).writeAsStringSync(jsContent.replaceFirst(
-        "from 'dart_sdk'", "from '${uriPathForwardSlashed(jsSdkPath)}'"));
+        "from 'dart_sdk.js'", "from '${uriPathForwardSlashed(jsSdkPath)}'"));
 
     if (debugging) {
       createHtmlWrapper(

pkg/dev_compiler/test/sourcemap/sourcemaps_ddk_suite.dart

@@ -89,7 +89,7 @@ class DevCompilerRunner implements CompilerRunner {
 
     var jsContent = File.fromUri(outputFile).readAsStringSync();
     File.fromUri(outputFile).writeAsStringSync(jsContent.replaceFirst(
-        "from 'dart_sdk'", "from '${uriPathForwardSlashed(jsSdkPath)}'"));
+        "from 'dart_sdk.js'", "from '${uriPathForwardSlashed(jsSdkPath)}'"));
 
     if (debugging) {
       createHtmlWrapper(

pkg/dev_compiler/tool/ddb

@@ -236,6 +236,15 @@ void main(List<String> args) async {
         nodeBinary, ['--inspect=localhost:$port', nodeFile],
         environment: {'NODE_PATH': nodePath});
   } else if (d8) {
+    // Fix SDK import.  `d8` doesn't let us set paths, so we need a full path
+    // to the SDK.
+
+    var jsFile = File('$libRoot/$basename.js');
+    var jsContents = jsFile.readAsStringSync();
+    jsContents = jsContents.replaceFirst(
+        "from 'dart_sdk.js'", "from '$sdkJsPath/dart_sdk.js'");
+    jsFile.writeAsStringSync(jsContents);
+
     var runjs = '''
     import { dart, _isolate_helper } from '$sdkJsPath/dart_sdk.js';
     import { $basename } from '$basename.js';