Fix issue in CpuTimePerUid where microseconds are used as milliseconds

KernelUidCpuTimeReader reads microseconds, but they are written to a
millisecond field in atoms.proto. Introduced in ag/3693225.

See google3 change: cl/222044203

Test: build
Bug: 119853118
Change-Id: I170e996aa852e28a246a98226677907bb3560371
diff --git a/atoms.proto b/atoms.proto
index e12b665..281f900 100644
--- a/atoms.proto
+++ b/atoms.proto
@@ -1794,8 +1794,8 @@
  */
 message CpuTimePerUid {
     optional int32 uid = 1 [(is_uid) = true];
-    optional uint64 user_time_millis = 2;
-    optional uint64 sys_time_millis = 3;
+    optional uint64 user_time_micros = 2;
+    optional uint64 sys_time_micros = 3;
 }
 
 /**