Add support for transparent/translucent pixels in the user image

components/user_manager/user_image/user_image.h

 // 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.
 
 #ifndef COMPONENTS_USER_MANAGER_USER_IMAGE_USER_IMAGE_H_
 #define COMPONENTS_USER_MANAGER_USER_IMAGE_USER_IMAGE_H_
 
 #include <memory>
 #include <string>
 #include <vector>
 
 #include "base/files/file_path.h"
 #include "base/memory/ref_counted_memory.h"
 #include "components/user_manager/user_manager_export.h"
 #include "ui/gfx/image/image_skia.h"
 #include "url/gurl.h"
 
 namespace user_manager {
 
 // Wrapper class storing a still image and its bytes representation for
 // WebUI in a web-compatible format such as JPEG. Could be used for storing
 // profile images and user wallpapers.
 class USER_MANAGER_EXPORT UserImage {
  public:
-  // Encodes the given bitmap to bytes representation for WebUI. Returns null
-  // on failure.
-  static scoped_refptr<base::RefCountedBytes> Encode(const SkBitmap& bitmap);
+  // The format of the user image's bytes representation. PNG can support
+  // transparent background that's not supported with JPEG.
+  enum ImageFormat {
+    FORMAT_JPEG,
+    FORMAT_PNG,
+    FORMAT_UNKNOWN,
+  };
+
+  // Encodes the given bitmap to bytes representation in |image_format| for
+  // WebUI. Returns nullptr on failure.
+  static scoped_refptr<base::RefCountedBytes> Encode(const SkBitmap& bitmap,
+                                                     ImageFormat image_format);
 
   // Creates a new instance from a given still frame and tries to encode it
-  // to bytes representation for WebUI. Always returns a non-null result.
+  // to bytes representation in |image_format| for WebUI. Always returns a
+  // non-null result.
   // TODO(ivankr): remove eventually.
   static std::unique_ptr<UserImage> CreateAndEncode(
-      const gfx::ImageSkia& image);
+      const gfx::ImageSkia& image,
+      ImageFormat image_format);
+
+  // Choose the image format suitable for the given bitmap. Returns
+  // FORMAT_PNG if the bitmap contains transparent/translucent
+  // pixels. Otherwise, returns FORMAT_JPEG.
+  static ImageFormat ChooseImageFormat(const SkBitmap& bitmap);
 
   // Create instance with an empty still frame and no bytes
   // representation for WebUI.
   UserImage();
 
   // Creates a new instance from a given still frame without any bytes
   // representation for WebUI.
   explicit UserImage(const gfx::ImageSkia& image);
 
   // Creates a new instance from a given still frame and bytes
   // representation for WebUI.
   UserImage(const gfx::ImageSkia& image,
-            scoped_refptr<base::RefCountedBytes> image_bytes);
+            scoped_refptr<base::RefCountedBytes> image_bytes,
+            ImageFormat image_format);
 
   virtual ~UserImage();
 
   const gfx::ImageSkia& image() const { return image_; }
 
   // Optional bytes representation of the still image for WebUI.
   bool has_image_bytes() const { return image_bytes_ != nullptr; }
   scoped_refptr<base::RefCountedBytes> image_bytes() const {
     return image_bytes_;
   }
+  // Format of the bytes representation.
+  ImageFormat image_format() const { return image_format_; }
 
   // URL from which this image was originally downloaded, if any.
   void set_url(const GURL& url) { url_ = url; }
   GURL url() const { return url_; }
 
   // Whether |image_bytes| contains data in format that is considered safe to
   // decode in sensitive environment (on Login screen).
   bool is_safe_format() const { return is_safe_format_; }
   void MarkAsSafe();
 
   const base::FilePath& file_path() const { return file_path_; }
   void set_file_path(const base::FilePath& file_path) {
     file_path_ = file_path;
   }
 
  private:
   gfx::ImageSkia image_;
   scoped_refptr<base::RefCountedBytes> image_bytes_;
   GURL url_;
 
   // If image was loaded from the local file, file path is stored here.
   base::FilePath file_path_;
   bool is_safe_format_ = false;
+  ImageFormat image_format_ = FORMAT_UNKNOWN;
 
   DISALLOW_COPY_AND_ASSIGN(UserImage);
 };
 
 }  // namespace user_manager
 
 #endif  // COMPONENTS_USER_MANAGER_USER_IMAGE_USER_IMAGE_H_