Set up background memory light tracing field trials

chrome/browser/tracing/navigation_tracing.cc

Index: chrome/browser/tracing/navigation_tracing.cc
diff --git a/chrome/browser/tracing/navigation_tracing.cc b/chrome/browser/tracing/navigation_tracing.cc
index 83f55c5fe4a597d160a5fc5fe07ba92633a770e2..b764e2b1f2e97001b9b4396fcbd589fdce5373b5 100644
--- a/chrome/browser/tracing/navigation_tracing.cc
+++ b/chrome/browser/tracing/navigation_tracing.cc
@@ -82,6 +82,18 @@ void SetupNavigationTracing() {
     rules_dict->SetInteger("histogram_upper_value", 10000);
     rules_list->Append(std::move(rules_dict));
   }
+  {
+    std::unique_ptr<base::DictionaryValue> rules_dict(
+        new base::DictionaryValue());
+    rules_dict->SetString("rule",
+                          "MONITOR_AND_DUMP_WHEN_SPECIFIC_HISTOGRAM_AND_VALUE");
+    rules_dict->SetString("category", "BENCHMARK_MEMORY_LIGHT");
+    rules_dict->SetString("histogram_name", "V8.GCLowMemoryNotification");

[ssid, 2016/06/02 00:14:15]

Not sure why I should write the rules for low memory trigger inside
"navigation_tracing" file. How are they related?

[oystein (OOO til 10th of July), 2016/06/02 06:11:33]

Unfortunate legacy naming. Navigation tracing is what deep reports is called in
the about://flags entry, even though there's nothing in the system that
restricts it to navigation traces; it's just what it was initially used for. It
should probably be renamed, if someone can come up with a good alternative :).

[oystein (OOO til 10th of July), 2016/06/02 06:11:33]

Also: Two different trigger with the same conditions won't work; the second one
to trigger will stop the trace. Maybe the histogram values to trigger on can be
two discrete ranges, if this is to test the pipeline?

[ssid, 2016/06/03 06:34:33]

Sorry about this confusion. This rule shouldn't be in navigation tracing file. I
will later add this if needed.

+    rules_dict->SetInteger("trigger_delay", 30);
+    rules_dict->SetInteger("histogram_lower_value", 0);
+    rules_dict->SetInteger("histogram_upper_value", 10000);
+    rules_list->Append(std::move(rules_dict));
+  }
   dict.Set("configs", std::move(rules_list));
 
   std::unique_ptr<content::BackgroundTracingConfig> config(