Add device trust key pair into BrowserReport

Bug: 1148561
Change-Id: I77051c7af4f9ca67d954d31d2ce7a596b2b89a58
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2535670Reviewed-by: Owen Min <zmin@chromium.org>
Reviewed-by: Albert J. Wong <ajwong@chromium.org>
Commit-Queue: Alice Gong <alicego@google.com>
Cr-Commit-Position: refs/heads/master@{#828352}

components/policy/proto/device_management_backend.proto

@@ -1923,6 +1923,8 @@ message ChromeDesktopReportRequest {
   // information. When list is empty or unset, the report should contains all
   // information.
   repeated PartialReportType partial_report_types = 10;
+  // Public key that can be used for attesting the machine.
+  optional string machine_attestation_key = 11;
 }
 
 // Report user level status on Chrome OS platform. Chrome OS equivalent of