Remove use of cwd in d8 preamble

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

Index: sdk/lib/_internal/js_runtime/lib/preambles/d8.js
diff --git a/sdk/lib/_internal/js_runtime/lib/preambles/d8.js b/sdk/lib/_internal/js_runtime/lib/preambles/d8.js
index 75c0c459003976edd60f515b01f5719fc2d4ab09..ca9093756e46bee93a6cdc15d041a9c7a6811376 100644
--- a/sdk/lib/_internal/js_runtime/lib/preambles/d8.js
+++ b/sdk/lib/_internal/js_runtime/lib/preambles/d8.js
@@ -16,21 +16,13 @@ if (typeof global != "undefined") self = global;  // Node.js.
 
   // Location (Uri.base)
 
-  var workingDirectory;
-  // TODO(sgjesse): This does not work on Windows.
-  if (typeof os == "object" && "system" in os) {
-    // V8.
-    workingDirectory = os.system("pwd");
-    var length = workingDirectory.length;
-    if (workingDirectory[length - 1] == '\n') {
-      workingDirectory = workingDirectory.substring(0, length - 1);
-    }
-  } else if (typeof process != "undefined" &&
+  var baseUri = 'org-dartlang-d8-preamble:///mock/uri/base/';
+  if (typeof process != "undefined" &&
              typeof process.cwd == "function") {
     // Node.js.
-    workingDirectory = process.cwd();
+    baseUri = 'file://' + process.cwd() + '/';
   }
-  self.location = { href: "file://" + workingDirectory + "/" };
+  self.location = { href: baseUri };
 
   // Event loop.