Fix an issue that download file is not deleted when clicking Replace button

Fix an issue that download file is not deleted when clicking Replace button

When enqueueing a file to Android DownloadManager, we delete the file if
user choose to overwrite.
But when using Chrome's network stack, we didn't remove the file.
This will reduce user's sdcard space during download.
And it also causes issues when user try to resume the download.
This CL deletes the file when user clicks the "Replace File" button.

TBR=yfriedman@chromium.org
BUG=602721
Review URL: https://codereview.chromium.org/1884783002

Cr-Commit-Position: refs/heads/master@{#387368}
(cherry picked from commit c0258fd32bb4bda3ab721d426c3c4a73177af861)

Committed: https://chromium.googlesource.com/chromium/src/+/d3fbb31663558ab79ed42d101bd0cb8587c5cea3

[qinmin, 2016-04-14 19:27:12]

Description was changed from

==========
Fix an issue that download file is not deleted when clicking Replace button

When enqueueing a file to Android DownloadManager, we delete the file if
user choose to overwrite.
But when using Chrome's network stack, we didn't remove the file.
This will reduce user's sdcard space during download.
And it also causes issues when user try to resume the download.
This CL deletes the file when user clicks the "Replace File" button.

TBR=yfriedman@chromium.org
BUG=602721

Review URL: https://codereview.chromium.org/1884783002

Cr-Commit-Position: refs/heads/master@{#387368}
(cherry picked from commit c0258fd32bb4bda3ab721d426c3c4a73177af861)
==========

to

==========
Fix an issue that download file is not deleted when clicking Replace button

When enqueueing a file to Android DownloadManager, we delete the file if
user choose to overwrite.
But when using Chrome's network stack, we didn't remove the file.
This will reduce user's sdcard space during download.
And it also causes issues when user try to resume the download.
This CL deletes the file when user clicks the "Replace File" button.

TBR=yfriedman@chromium.org
BUG=602721

Review URL: https://codereview.chromium.org/1884783002

Cr-Commit-Position: refs/heads/master@{#387368}
(cherry picked from commit c0258fd32bb4bda3ab721d426c3c4a73177af861)

Committed:
https://chromium.googlesource.com/chromium/src/+/d3fbb31663558ab79ed42d101bd0...
==========

[qinmin, 2016-04-14 19:27:14]

Committed patchset #1 (id:1) manually as
d3fbb31663558ab79ed42d101bd0cb8587c5cea3 (presubmit successful).