Tag CSP violation reports as CSP reports, not as ping

BUG=637577
TEST=./browser_tests --gtest_filter=ExtensionWebRequestApiTest.WebRequestTypes

Review-Url: https://codereview.chromium.org/2402233002
Cr-Original-Commit-Position: refs/heads/master@{#450329}
Committed: https://chromium.googlesource.com/chromium/src/+/ac2c8350c76da73e48d8ed582c85fd8f572b54d5
Review-Url: https://codereview.chromium.org/2402233002
Cr-Commit-Position: refs/heads/master@{#451637}
7 files changed