Expose computation of md5 content checksums for files via a file manager private API.

chrome/test/data/extensions/api_test/file_browser/content_checksum_test/test.js

Index: chrome/test/data/extensions/api_test/file_browser/content_checksum_test/test.js
diff --git a/chrome/test/data/extensions/api_test/file_browser/content_checksum_test/test.js b/chrome/test/data/extensions/api_test/file_browser/content_checksum_test/test.js
new file mode 100644
index 0000000000000000000000000000000000000000..3e3c34e025aaf9f3c56c6f5cd4f0ded71d7be343
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+++ b/chrome/test/data/extensions/api_test/file_browser/content_checksum_test/test.js
@@ -0,0 +1,54 @@
+// Copyright (c) 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/**
+ * The test file system should be created and populated before running the test
+ * extension.
+ *
+ * The only file used right now is <root>/test_dir/test_file.txt.
+ */
+
+// This is a golden value computed using the md5sum command line tool.
+var kExpectedHash = 'a3dfffb5a580272fb8986611a9dbd166';
+
+function getTestFilesystem() {
+  return new Promise(function(resolve, reject) {
+    chrome.fileManagerPrivate.getVolumeMetadataList(
+        function(volumeMetadataList) {
+          var testVolume = volumeMetadataList.filter(function(volume) {
+            return volume.volumeType === 'testing';
+          })[0];
+
+          chrome.fileManagerPrivate.requestFileSystem(
+              testVolume.volumeId,
+              function(fileSystem) {
+                if (!fileSystem) {
+                  reject(new Error('Failed to acquire the testing volume.'));
+                }
+                resolve(fileSystem);
+              });
+        });
+  });
+}
+
+// Run the tests.
+getTestFilesystem().then(
+    function(fileSystem) {
+      chrome.test.runTests([
+          // Checks the checksum code using a golden file.
+          function testGoldenChecksum() {
+            fileSystem.root.getFile(
+                'test_dir/test_file.txt',
+                {create: false},
+                function(entry) {
+                  chrome.fileManagerPrivate.computeChecksum(
+                      entry.toURL(),
+                      chrome.test.callbackPass(function(result) {
+                        chrome.test.assertEq(kExpectedHash, result);
+                      }));
+                },
+                chrome.test.fail);
+          }
+      ]);
+    });