No prompt if the storage isn't enough while downloading.

[freya zhang]

Information:
current build number: 216
device name: arale
channel: ubuntu-touch/rc-proposed/meizu.zh-proposed
last update: 2016-01-15 02:48:04
version version: 215
version ubuntu: 20160114
version device: 20160111-51982fc
version custom: 1452528000

Precondition:
The device storage is close to full

Steps:
1.Launch browser and visit website: http://people.canonical.com/~wsy324/downloadtest/
2.Select a file to download (which will exceed the storage usage)
3.Go to browser settings->Download and observe
4.Tap on "Cancel" button of current downloading and observe

Actual result:
After step 3, the progress bar stops and no prompt to inform user what happens
After step 4, tapping on Cancel button can do nothing

Expected result:
Prompt message like "the storage is not enough.." and user can cancel current downloading

Notes:In fact , when the storage is close to full, only you restart the phone,the prompt will display

[Pat McGowan (pat-mcgowan)]

@freya can you check if this is a dupe of bug #1414037

[freya zhang (572747629-b)]

This is a dupe of bug #1414037 after I check.