Use BlobCallback in toBlob instead of FileCallback

third_party/WebKit/Source/core/fileapi/BlobCallback.idl

Index: third_party/WebKit/Source/core/fileapi/BlobCallback.idl
diff --git a/third_party/WebKit/Source/core/fileapi/FileCallback.idl b/third_party/WebKit/Source/core/fileapi/BlobCallback.idl
similarity index 95%
copy from third_party/WebKit/Source/core/fileapi/FileCallback.idl
copy to third_party/WebKit/Source/core/fileapi/BlobCallback.idl
index 2a692ba166d82a4ce38c60ca81452a65e61ee5d8..e3ebb5e6f2e28c6decb0772c73a802812de17f77 100644
--- a/third_party/WebKit/Source/core/fileapi/FileCallback.idl
+++ b/third_party/WebKit/Source/core/fileapi/BlobCallback.idl
@@ -28,6 +28,6 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-callback interface FileCallback {
-    void handleEvent(File file);
+callback interface BlobCallback {

[philipj_slow, 2016/01/19 22:28:14]

Actually, the conclusion of
http://code.google.com/p/chromium/issues/detail?id=569301 was that callback
functions already *are* supported, but missing some of the convenience of
callback interfaces.

Since it should already be possible to use a callback function, can you try
doing that and see if there's any trouble. It would be sad to introduce a new
callback interface if it can be avoided.

+    void handleEvent(Blob? blob);
 };