GitLab

- declare BuildJSONValue in report_body as virtual
- make all sub-class implement override implementation

add toJSON to report_body, making it serializable

- Includes 4 different reports
- and parent class LocationReportBody

Bug: 917945
Change-Id: I2ef281aad171ec6a477ae562fab3257847ee4f41
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1895957Reviewed-by: David Bokan <bokan@chromium.org>
Reviewed-by: Jason Chase <chasej@chromium.org>
Commit-Queue: Rodney Ding <rodneyding@google.com>
Cr-Commit-Position: refs/heads/master@{#714244}