fetchInlineImages should be split into multiple tasks.

[tdresser]

async fetchInlineImages_(attachments: ImageAttachmentData[]) {
for (let attachmentData of attachments) {
let fetched = await gapi.client.gmail.users.messages.attachments.get({
'id': attachmentData.attachment.id,
'messageId': this.id,
'userId': USER_ID,
});
let data = Message.base64_.decode(fetched.result.data || '');
attachmentData.image.src =
data:${attachmentData.attachment.contentType},${data};
}
}

Ojan: I would expect a real yield when making that gapi call. Maybe this is microtasks doing something terrible?