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..fc2278d2037b6eac19ecb80bd533f2d0206bbb38 100644
--- a/tools/perf/metrics/cpu.py
+++ b/tools/perf/metrics/cpu.py
@@ -3,6 +3,7 @@
 # found in the LICENSE file.
 
 from metrics import Metric
+from telemetry.value import improvement_direction
 from telemetry.value import scalar
 
 
@@ -37,7 +38,8 @@ 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,
+          improvement_direction=improvement_direction.DOWN))
 
 
 def _SubtractCpuStats(cpu_stats, start_cpu_stats):