dart2js: compute the currentScript in the preamble for d8 and jsshell.

sdk/lib/_internal/compiler/js_lib/preambles/d8.js

Index: sdk/lib/_internal/compiler/js_lib/preambles/d8.js
diff --git a/sdk/lib/_internal/compiler/js_lib/preambles/d8.js b/sdk/lib/_internal/compiler/js_lib/preambles/d8.js
index a48f918cf704bde5d69786c81e3453b10fdffad2..18823e15d9dbaa7953d439d40a6415c493b289c7 100644
--- a/sdk/lib/_internal/compiler/js_lib/preambles/d8.js
+++ b/sdk/lib/_internal/compiler/js_lib/preambles/d8.js
@@ -281,6 +281,43 @@ if (typeof global != "undefined") self = global;  // Node.js.
   self.clearInterval = cancelTimer;
   self.scheduleImmediate = addTask;
 
+  function computeCurrentScript() {
+    try {
+      throw new Error();
+    } catch(e) {
+      var stack = e.stack;
+      // The V8 stack looks like:
+      //    at computeCurrentScript (preambles/d8.js:286:13)
+      //    at Object.currentScript (preambles/d8.js:308:31)
+      //    at init.currentScript (/tmp/foo.js:308:19)
+      //    at /tmp/foo.js:320:7
+      //    at /tmp/foo.js:331:4
+      var re = new RegExp("^ *at [^(]*\\((.*):[0-9]*:[0-9]*\\)$", "mg");
+      var lastMatch = null;
+      do {
+        var match = re.exec(stack);
+        if (match != null) lastMatch = match;
+      } while (match != null);
+      return lastMatch[1];
+    }
+  }
+
+  // Adding a 'document' is dangerous since it invalidates the 'typeof document'
+  // test to see if we are running in the browser. It means that the runtime
+  // needs to do more precise checks.
+  // Note that we can't run "currentScript" right away, since that would give
+  // us the location of the preamble file. Instead we wait for the first access
+  // which should happen just before invoking main. At this point we are in
+  // the main file and setting the currentScript property is correct.
+  var cachedCurrentScript = null;
+  self.document = { get currentScript() {
+      if (cachedCurrentScript == null) {
+        cachedCurrentScript = {src: computeCurrentScript()};
+      }
+      return cachedCurrentScript;
+    }
+  };
+
   // Support for deferred loading.
   self.dartDeferredLibraryLoader = function(uri, successCallback, errorCallback) {
     try {