Consume the first sample of KernelUidCpuTimeReader

If the system_server crashes, when it starts back up
it will assume that the entries in kernelUidCpuTimeReader
are all fresh and we will end up double counting cpu time
and power.

Bug:29163081
Change-Id: I73e693199c170229af57efd610950e90263ac9bc

core/java/com/android/internal/os/KernelUidCpuTimeReader.java

@@ -84,7 +84,8 @@ public class KernelUidCpuTimeReader {
                     powerMaUs = 0;
                 }
 
-                if (callback != null) {
+                // Only report if there is a callback and if this is not the first read.
+                if (callback != null && mLastTimeReadUs != 0) {
                     long userTimeDeltaUs = userTimeUs;
                     long systemTimeDeltaUs = systemTimeUs;
                     long powerDeltaMaUs = powerMaUs;