Called before a download begins. |suggested_name| is the suggested name
for the download file. Return true (1) and execute |callback| either
asynchronously or in this function to continue or cancel the download.
Return false (0) to proceed with default handling (cancel with Alloy
style, download shelf with Chrome style). Do not keep a reference to
|download_item| outside of this function.
Called before a download begins. |suggested_name| is the suggested name for the download file. Return true (1) and execute |callback| either asynchronously or in this function to continue or cancel the download. Return false (0) to proceed with default handling (cancel with Alloy style, download shelf with Chrome style). Do not keep a reference to |download_item| outside of this function.