[dart2js] allow tabs when computing the current script.

For unclear reasons, a JS stack trace sometimes has tabs instead of
spaces. For example, this has been observed when using the VS Code
extension host (NodeJs) in issue #55684.  When that happens, the d8
preamble function to compute the current script fails. While tabs are
not generally present there, this small change can make the logic a bit
more robust and versatile.

Fixes #55684

Change-Id: Id1833a8b550a0ba5c9822e98d9e69ea9abfd6232
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/366160
Reviewed-by: Nicholas Shahan <nshahan@google.com>
Reviewed-by: Nate Biggs <natebiggs@google.com>
Commit-Queue: Sigmund Cherem <sigmund@google.com>

sdk/lib/_internal/js_dev_runtime/private/preambles/d8.js

@@ -305,12 +305,13 @@ if (typeof global != "undefined") self = global;  // Node.js.
       //    at init.currentScript (/tmp/foo.js:308:19)
       //    at /tmp/foo.js:320:7
       //    at /tmp/foo.js:331:4
-      // Sometimes the 'init.currentScript' line is in the format without the
+      // Sometimes the leading spaces are tabs (http://dartbug.com/55684) and
+      // sometimes the 'init.currentScript' line is in the format without the
       // function name, so match with or without parentheses.
 
-      //              vvvvvvvvvvvv Optional prefix up to '('.
-      var re = /^ *at (?:[^(]*\()?(.*):[0-9]*:[0-9]*\)?$/mg
-      //              Optional ')' at end           ^^^
+      //               vvvvvvvvvvvv Optional prefix up to '('.
+      var re = /^\s*at (?:[^(]*\()?(.*):[0-9]*:[0-9]*\)?$/mg
+      //               Optional ')' at end           ^^^
 
       var lastMatch = null;
       do {

sdk/lib/_internal/js_runtime/lib/preambles/d8.js

@@ -298,12 +298,13 @@ if (typeof global != "undefined") self = global;  // Node.js.
       //    at init.currentScript (/tmp/foo.js:308:19)
       //    at /tmp/foo.js:320:7
       //    at /tmp/foo.js:331:4
-      // Sometimes the 'init.currentScript' line is in the format without the
+      // Sometimes the leading spaces are tabs (http://dartbug.com/55684) and
+      // sometimes the 'init.currentScript' line is in the format without the
       // function name, so match with or without parentheses.
 
-      //              vvvvvvvvvvvv Optional prefix up to '('.
-      var re = /^ *at (?:[^(]*\()?(.*):[0-9]*:[0-9]*\)?$/mg
-      //              Optional ')' at end           ^^^
+      //               vvvvvvvvvvvv Optional prefix up to '('.
+      var re = /^\s*at (?:[^(]*\()?(.*):[0-9]*:[0-9]*\)?$/mg
+      //               Optional ')' at end           ^^^
 
       var lastMatch = null;
       do {