Benchmark: `--save-all-traces` argument

apps/benchmark/benchmark_app.cc

Index: apps/benchmark/benchmark_app.cc
diff --git a/apps/benchmark/benchmark_app.cc b/apps/benchmark/benchmark_app.cc
index bfdc2998797f59a7cad54bf48fbf6771038267e0..7a3db357894ed9b2796656591cc80d2deebe1f9b 100644
--- a/apps/benchmark/benchmark_app.cc
+++ b/apps/benchmark/benchmark_app.cc
@@ -44,17 +44,11 @@ class BenchmarkApp : public mojo::ApplicationDelegate,
       return;
     }
 
-    // Calculate a list of trace categories we want to collect: a union of all
-    // categories targeted in measurements.
-    std::set<std::string> category_set;
-    for (const Measurement& measurement : args_.measurements) {
-      std::vector<std::string> categories;
-      base::SplitString(measurement.target_event.categories, ',', &categories);
-      category_set.insert(categories.begin(), categories.end());
+    // Don't compute the categories string if all categories should be traced.
+    std::string categories_str = "*";
+    if (!args_.write_output_file) {

[ppi, 2015/10/29 16:02:09]

nit: it's a bit weird to set the initial value to a special case, and then flip
the value in the default case

Can you declare the variable without setting anything, and then to:

if (args_.write_output_file) {
  one thing
} else {
  another thing
}

?

Alternatively you can use the ternary operator.

[nelly, 2015/10/29 16:48:22]

Done.

+      categories_str = ComputeCategoriesStr();
     }
-    std::vector<std::string> unique_categories(category_set.begin(),
-                                               category_set.end());
-    std::string categories_str = JoinString(unique_categories, ',');
 
     // Connect to trace collector, which will fetch the trace events produced by
     // the app being benchmarked.
@@ -66,10 +60,23 @@ class BenchmarkApp : public mojo::ApplicationDelegate,
 
     // Start tracing the application with 1 sec of delay.
     base::MessageLoop::current()->PostDelayedTask(
-        FROM_HERE,
-        base::Bind(&BenchmarkApp::StartTracedApplication,
-            base::Unretained(this), app),
-        base::TimeDelta::FromSeconds(1));
+        FROM_HERE, base::Bind(&BenchmarkApp::StartTracedApplication,
+                              base::Unretained(this), app),
+        base::TimeDelta::FromMilliseconds(1000));

[ppi, 2015/10/29 16:02:09]

Why the change from s to ms?

[nelly, 2015/10/29 16:48:22]

Done.

+  }
+
+  // Computes the string of trace categories we want to collect: a union of all
+  // categories targeted in measurements.
+  std::string ComputeCategoriesStr() {
+    std::set<std::string> category_set;
+    for (const Measurement& measurement : args_.measurements) {
+      std::vector<std::string> categories;
+      base::SplitString(measurement.target_event.categories, ',', &categories);
+      category_set.insert(categories.begin(), categories.end());
+    }
+    std::vector<std::string> unique_categories(category_set.begin(),
+                                               category_set.end());
+    return JoinString(unique_categories, ',');
   }
 
   void StartTracedApplication(mojo::ApplicationImpl* app) {