Background tracing: Added trace_chance

content/browser/tracing/background_tracing_rule.h

Index: content/browser/tracing/background_tracing_rule.h
diff --git a/content/browser/tracing/background_tracing_rule.h b/content/browser/tracing/background_tracing_rule.h
index c5407ba83b11df5b3bca25d0442558efb7fb0cad..6e85836ccb305b197d01c3c315705a01291c0169 100644
--- a/content/browser/tracing/background_tracing_rule.h
+++ b/content/browser/tracing/background_tracing_rule.h
@@ -20,7 +20,8 @@ class CONTENT_EXPORT BackgroundTracingRule {
   virtual ~BackgroundTracingRule();
 
   virtual void Install() {}
-  virtual void IntoDict(base::DictionaryValue* dict) const = 0;
+  virtual void IntoDict(base::DictionaryValue* dict) const;
+  void Setup(const base::DictionaryValue* dict);
   virtual bool ShouldTriggerNamedEvent(const std::string& named_event) const;
   virtual BackgroundTracingConfigImpl::CategoryPreset GetCategoryPreset() const;
   virtual void OnHistogramTrigger(const std::string& histogram_name) const {}
@@ -28,6 +29,9 @@ class CONTENT_EXPORT BackgroundTracingRule {
   // Seconds from the rule is triggered to finalization should start.
   virtual int GetTraceTimeout() const;
 
+  // Probability that we should allow a tigger to  happen.
+  double trigger_chance() const { return trigger_chance_; }
+
   static scoped_ptr<BackgroundTracingRule> PreemptiveRuleFromDict(
       const base::DictionaryValue* dict);
 
@@ -37,6 +41,8 @@ class CONTENT_EXPORT BackgroundTracingRule {
 
  private:
   DISALLOW_COPY_AND_ASSIGN(BackgroundTracingRule);
+
+  double trigger_chance_;
 };
 
 }  // namespace content