Submit a sample of notification images to Safe Browsing

These will be scanned for social engineering behavior.

Only uploads if all of the following are true:
- User has opted in to SBER_LEVEL_SCOUT.
- Origin is not on CSD phishing whitelist.
- Device has sent < 5 reports in last 24 hours (see persistence TODO).
- Device is part of the enabled experiment group.

The notification image bitmap is downscaled to <= 512x512, encoded as a
PNG, then sent to the CSD server as a NotificationImageReportRequest
protobuf from chrome/common/safe_browsing/csd.proto.

BUG=678443

Review-Url: https://codereview.chromium.org/2637153002
Cr-Commit-Position: refs/heads/master@{#445365}
diff --git a/chrome/browser/BUILD.gn b/chrome/browser/BUILD.gn
index 8991997..094508f 100644
--- a/chrome/browser/BUILD.gn
+++ b/chrome/browser/BUILD.gn
@@ -1993,6 +1993,8 @@
       "safe_browsing/certificate_reporting_service.h",
       "safe_browsing/certificate_reporting_service_factory.cc",
       "safe_browsing/certificate_reporting_service_factory.h",
+      "safe_browsing/notification_image_reporter.cc",
+      "safe_browsing/notification_image_reporter.h",
       "safe_browsing/permission_reporter.cc",
       "safe_browsing/permission_reporter.h",
       "safe_browsing/ping_manager.cc",