Gallery.app : Truncates the file after a blob of new image is created.

ui/file_manager/gallery/js/gallery_item.js

 // Copyright 2014 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.
 
 /**
  * Object representing an image item (a photo).
  *
  * @param {!FileEntry} entry Image entry.
  * @param {!EntryLocation} locationInfo Entry location information.
  * @param {!MetadataItem} metadataItem
@@ skipping 242 matching lines @@
   }.bind(this);
 
   var onError = function(error) {
     console.error('Error saving from gallery', name, error);
     ImageUtil.metrics.recordEnum(ImageUtil.getMetricName('SaveResult'), 0, 2);
     if (callback)
       callback(false);
   };
 
   var doSave = function(newFile, fileEntry) {
-    var metadataPromise = metadataModel.get(
+    var blob;
+    var fileWriter;
+
+    metadataModel.get(
         [fileEntry],
-        ['mediaMimeType', 'contentMimeType', 'ifd', 'exifLittleEndian']);
-    metadataPromise.then(function(metadataItems) {
-      fileEntry.createWriter(function(fileWriter) {
-        var writeContent = function() {
-          fileWriter.onwriteend = onSuccess.bind(null, fileEntry);
-          var metadataItem = metadataItems[0];
-          metadataItem.modificationTime = new Date();
-          var metadataEncoder = ImageEncoder.encodeMetadata(
-              metadataItem, canvas, /* quality for thumbnail*/ 0.8);
-          // Contrary to what one might think 1.0 is not a good default. Opening
-          // and saving an typical photo taken with consumer camera increases
-          // its file size by 50-100%. Experiments show that 0.9 is much better.
-          // It shrinks some photos a bit, keeps others about the same size, but
-          // does not visibly lower the quality.
-          fileWriter.write(ImageEncoder.getBlob(canvas, metadataEncoder, 0.9));
-        }.bind(this);
-        fileWriter.onerror = function(error) {
-          onError(error);
-          // Disable all callbacks on the first error.
-          fileWriter.onerror = null;
-          fileWriter.onwriteend = null;
-        };
-        if (newFile) {
-          writeContent();
+        ['mediaMimeType', 'contentMimeType', 'ifd', 'exifLittleEndian']
+    ).then(function(metadataItems) {
+      // Create the blob of new image.
+      var metadataItem = metadataItems[0];
+      metadataItem.modificationTime = new Date();
+      var metadataEncoder = ImageEncoder.encodeMetadata(
+          metadataItem, canvas, /* quality for thumbnail*/ 0.8);
+      // Contrary to what one might think 1.0 is not a good default. Opening
+      // and saving an typical photo taken with consumer camera increases
+      // its file size by 50-100%. Experiments show that 0.9 is much better.
+      // It shrinks some photos a bit, keeps others about the same size, but
+      // does not visibly lower the quality.
+      blob = ImageEncoder.getBlob(canvas, metadataEncoder, 0.9);
+    }).then(function() {
+      // Create writer.
+      return new Promise(function(fullfill, reject) {
+        fileEntry.createWriter(fullfill, reject);
+      });
+    }).then(function(writer) {
+      fileWriter = writer;
+
+      // Truncates the file to 0 byte if it overwrites.
+      return new Promise(function(fulfill, reject) {
+        if (!newFile) {
+          fileWriter.onerror = reject;
+          fileWriter.onwriteend = fulfill;
+          fileWriter.truncate(0);
         } else {
-          fileWriter.onwriteend = writeContent;
-          fileWriter.truncate(0);
+          fulfill(null);
         }
-      }.bind(this), onError);
-    }.bind(this));
+      });
+    }).then(function() {
+      // Writes the blob of new image.
+      return new Promise(function(fulfill, reject) {
+        fileWriter.onerror = reject;
+        fileWriter.onwriteend = fulfill;
+        fileWriter.write(blob);
+      });
+    }).then(onSuccess.bind(null, fileEntry))
+    .catch(function(error) {
+      onError(error);
+      // Disable all callbacks on the first error.
+      fileWriter.onerror = null;
+      fileWriter.onwriteend = null;
+    });
   }.bind(this);
 
   var getFile = function(dir, newFile) {
     dir.getFile(name, {create: newFile, exclusive: newFile},
         function(fileEntry) {
           doSave(newFile, fileEntry);
         }.bind(this), onError);
   }.bind(this);
 
   var checkExistence = function(dir) {
@@ skipping 50 matching lines @@
         return Promise.reject(str('GALLERY_FILE_EXISTS'));
       }, function() {
         return new Promise(
             this.entry_.moveTo.bind(this.entry_, parentDirectory, newFileName));
       }.bind(this));
     }.bind(this));
   }.bind(this)).then(function(entry) {
     this.entry_ = entry;
   }.bind(this));
 };