[ddc] Add getSourceMap debugger API to dartDevEmbedder

This is used in bootstrappers to set a source map provider
within stack_trace_mapper.dart so that stack traces can be
mapped to their Dart equivalent.

Change-Id: If7dd7024cf8928f1b3a127599015107fcbafb2f4
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/405245
Reviewed-by: Nicholas Shahan <[email protected]>
Auto-Submit: Srujan Gaddam <[email protected]>
Commit-Queue: Srujan Gaddam <[email protected]>

Author: srujzs

pkg/dev_compiler/lib/js/ddc/ddc_module_loader.js

@@ -1927,6 +1927,16 @@ if (!self.deferred_loader) {
     stackTrace(error) {
       return dartRuntimeLibrary().stackTrace(error).toString();
     }
+
+    /**
+     * Returns the source map path for a given Dart file, if one was registered.
+     *
+     * @param {String} url The path of a Dart file.
+     * @returns {?String} The associated source map location if one exists.
+     */
+    getSourceMap(url) {
+      return dartRuntimeLibrary().getSourceMap(url);
+    }
   }
 
   const debugger_ = new Debugger();