Implement File constructor.

LayoutTests/fast/files/resources/blob-slice-common.js

+var blob, file; // Populated by runTests() in individual tests.
+var sliceParams = []; // Populated by individual tests.
+var testIndex = 0;
+
+function log(message)
+{
+    document.getElementById('console').appendChild(document.createTextNode(message + "\n"));
+}
+
+function testSlicing(start, end)
+{
+    var subBlob, subFile;
+    var blobReader = new FileReader();
+    var fileReader = new FileReader();
+    var message = "sliced ";
+    if (start == undefined && end == undefined) {
+        message += "without parameters";
+        subBlob = blob.slice();
+        subFile = file.slice();
+    } else if (end == undefined) {
+        message += "from " + start;
+        subBlob = blob.slice(start);
+        subFile = file.slice(start);
+    } else {
+        message += "from " + start + " to " + end;
+        subBlob = blob.slice(start, end);
+        subFile = file.slice(start, end);
+    }
+    message += ": ";
+    blobReader.onload = function(event) {
+        log("Blob " + message + event.target.result + ".");
+        fileReader.readAsText(subFile);
+    };
+    blobReader.onerror = function(event) {
+        log("Blob " + message + "error " + event.target.error.message);
+        fileReader.readAsText(subFile);
+    };
+    fileReader.onload = function(event) {
+        log("File " + message + event.target.result + ".");
+        runNextTest();
+    };
+    fileReader.onerror = function(event) {
+        log("File " + message + "error " + event.target.error.message);
+        runNextTest();
+    }
+    blobReader.readAsText(subBlob);
+}
+
+function runNextTest()
+{
+    if (testIndex >= sliceParams.length) {
+        if (window.testRunner)
+            testRunner.notifyDone();
+        return;
+    }
+
+    var start = sliceParams[testIndex][0];
+    var end = sliceParams[testIndex][1];
+    testIndex++;
+    testSlicing(start, end);
+}
+
+window.onerror = function(message)
+{
+    log("ERROR: " + message);
+    if (window.testRunner)
+        testRunner(notifyDone());
+}