chrome/browser/cryptauth: Set |device_display_diagonal_mils| in GcmDeviceInfo.

The backend requires this value to be set even though it is unused for
CrOS. This fixes device enrollment.

Bug: 76096024
Test: None, but E2E tests will be added shortly
Change-Id: Idbfcb61294f420a8eedf612d262b41df0428e432
Reviewed-on: https://chromium-review.googlesource.com/980814Reviewed-by: Jeremy Klein <jlklein@chromium.org>
Commit-Queue: James Hawkins <jhawkins@chromium.org>
Cr-Commit-Position: refs/heads/master@{#545830}

chrome/browser/chromeos/cryptauth/chrome_cryptauth_service.cc

@@ -93,8 +93,9 @@ cryptauth::GcmDeviceInfo GetGcmDeviceInfo() {
   // The Chrome OS version tracks the Chrome version, so fill in the same value
   // as |device_software_version_code|.
   device_info.set_device_os_version_code(software_version_code);
-  // |device_display_diagonal_mils| is unset because it only applies to
-  // phones/tablets.
+  // |device_display_diagonal_mils| is unused because it only applies to
+  // phones/tablets, but it must be set due to server API verification.
+  device_info.set_device_display_diagonal_mils(0);
 
   return device_info;
 }