Added support for improvement_direction to relevant values, which is propogated to chartjson.

tools/perf/metrics/cpu.py

Index: tools/perf/metrics/cpu.py
diff --git a/tools/perf/metrics/cpu.py b/tools/perf/metrics/cpu.py
index d0a03040f439246b258fa6ac3cb98c180d49f79b..bffd9c5e1c8acb7d9720dea5373059d0d910dd34 100644
--- a/tools/perf/metrics/cpu.py
+++ b/tools/perf/metrics/cpu.py
@@ -37,7 +37,7 @@ class CpuMetric(Metric):
       cpu_percent = 100 * cpu_stats[process_type]
       results.AddValue(scalar.ScalarValue(
           results.current_page, 'cpu_utilization.%s' % trace_name_for_process,
-          '%', cpu_percent, important=False))
+          '%', cpu_percent, important=False, higher_is_better=False))
 
 
 def _SubtractCpuStats(cpu_stats, start_cpu_stats):