Trigger clean-up GCs between tests of Speedometer

tools/perf/benchmarks/speedometer.py

Index: tools/perf/benchmarks/speedometer.py
diff --git a/tools/perf/benchmarks/speedometer.py b/tools/perf/benchmarks/speedometer.py
index 870895ee8ae78df788362df3fc949283bb0dbb61..ce97242cb1a19073ec1f7429da681a44c9279d8f 100644
--- a/tools/perf/benchmarks/speedometer.py
+++ b/tools/perf/benchmarks/speedometer.py
@@ -42,6 +42,7 @@ class SpeedometerMeasurement(page_test.PageTest):
 
   def CustomizeBrowserOptions(self, options):
     keychain_metric.KeychainMetric.CustomizeBrowserOptions(options)
+    options.AppendExtraBrowserArgs(['--js-flags=--expose_gc'])
 
   def ValidateAndMeasurePage(self, page, tab, results):
     tab.WaitForDocumentReadyStateToBeComplete()
@@ -58,6 +59,11 @@ class SpeedometerMeasurement(page_test.PageTest):
           benchmarkClient._measuredValues.push(measuredValues);
           benchmarkClient._timeValues.push(measuredValues.total);
         };
+        benchmarkClient.willRunTest = function(suite, test) {
+          for (var i = 0; i < 5; i++) {
+            gc();
+          }
+        };
         benchmarkClient.iterationCount = %d;
         startTest();
         """ % iterationCount)