@Yafei: reassigning to candice to work on as starter bug.

@Candice:
We currently keep a count of how many times we try a request before we give up. We keep a count of how many times we started a request for loading and how many times we failed. We count a download as failed when either we have started (and didn't finish) a request 5 or more times, or we have failed (encountered errors, etc) for 3 or more times, whichever comes first.

If a user pauses and resumes a download currently in progress 5 or more times, we will automatically fail the download.

The notification's "Pause" button eventually links to https://cs.chromium.org/chromium/src/components/offline_pages/core/downloads/download_ui_adapter.cc?rcl=e6eb32fc22a8ba0bc2765e38a5b5678855d86744&l=329

which goes to https://cs.chromium.org/chromium/src/components/offline_pages/core/background/request_coordinator.cc?rcl=3ab78ff221b5ee0065d89670f794b709e01fdfd6&l=439

We want to subtract 1 to the started attempt count of the request if it was the currently active request

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c367e9d9cac37c897fdc74c8e817efb61b0ba477

commit c367e9d9cac37c897fdc74c8e817efb61b0ba477
Author: Candice Sy <cmsy@google.com>
Date: Sat Mar 17 00:13:00 2018

Decrease the started_attempt_count_ for paused offlining requests.

This is a fix for the bug where 5 user pauses of an offlining request
fails the request because there is a max of 5 tries per request.
Decreasing the started_attempt_count_ when pausing an offlining request
undos the incrementation of the counter when the request began
offlining.

Bug:  701037 
Change-Id: I721b41bd9e9a1c366c9fe7f5896f5627e8d8fb1a
Reviewed-on: https://chromium-review.googlesource.com/957423
Commit-Queue: Candice Sy <cmsy@google.com>
Reviewed-by: Yafei Duan <romax@chromium.org>
Reviewed-by: Peter Williamson <petewil@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543879}
[modify] https://crrev.com/c367e9d9cac37c897fdc74c8e817efb61b0ba477/components/offline_pages/core/background/change_requests_state_task.cc
[modify] https://crrev.com/c367e9d9cac37c897fdc74c8e817efb61b0ba477/components/offline_pages/core/background/save_page_request.cc