IndexedDB: Fixed support for empty blobs.

content/browser/indexed_db/indexed_db_backing_store.cc

Index: content/browser/indexed_db/indexed_db_backing_store.cc
diff --git a/content/browser/indexed_db/indexed_db_backing_store.cc b/content/browser/indexed_db/indexed_db_backing_store.cc
index 4ae9ed4f236722b4c76dbcb62ee677b4223794c9..9a8421f5d403138c7110a97c7d720496aa337f10 100644
--- a/content/browser/indexed_db/indexed_db_backing_store.cc
+++ b/content/browser/indexed_db/indexed_db_backing_store.cc
@@ -2360,11 +2360,8 @@ class LocalWriteClosure : public FileWriterDelegate::DelegateWriteCallback,
                                  net::URLRequestContext* request_context) {
     DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::IO));
     scoped_ptr<storage::FileStreamWriter> writer(
-        storage::FileStreamWriter::CreateForLocalFile(
-            task_runner_.get(),
-            file_path,
-            0,
-            storage::FileStreamWriter::CREATE_NEW_FILE));
+        storage::FileStreamWriter::CreateForLocalFile(task_runner_.get(),
+                                                      file_path, 0));
     scoped_ptr<FileWriterDelegate> delegate(new FileWriterDelegate(
         writer.Pass(), storage::FlushPolicy::FLUSH_ON_COMPLETION));
 
@@ -2456,6 +2453,11 @@ bool IndexedDBBackingStore::WriteBlobFile(
     DCHECK(descriptor.url().is_valid());
     scoped_refptr<LocalWriteClosure> write_closure(
         new LocalWriteClosure(chained_blob_writer, task_runner_.get()));
+    {
+      // FileStreamWriter needs an existing file, so create one now.
+      base::File file(path,

[jsbell, 2015/03/03 01:01:48]

Should we do this in WriteBlobToFileOnIOThread instead, to avoid stalling the
IDB thread on this I/O?

[cmumford, 2015/03/03 22:26:09]

Can't do file I/O on that thread - only reason why it's here.

+                      base::File::FLAG_CREATE_ALWAYS | base::File::FLAG_WRITE);

[michaeln, 2015/03/03 00:02:51]

nit: ditto file.Close()

[cmumford, 2015/03/03 22:26:09]

Done.

+    }
     content::BrowserThread::PostTask(
         content::BrowserThread::IO,
         FROM_HERE,