Add a switch to emit browser histograms.

chrome/browser/ui/startup/startup_browser_creator.cc

Index: chrome/browser/ui/startup/startup_browser_creator.cc
diff --git a/chrome/browser/ui/startup/startup_browser_creator.cc b/chrome/browser/ui/startup/startup_browser_creator.cc
index 202f9f8f2c473aeddd0aa22a1a0214921d1e298b..3d434911d4237874872cf04cdd11d6240e80c590 100644
--- a/chrome/browser/ui/startup/startup_browser_creator.cc
+++ b/chrome/browser/ui/startup/startup_browser_creator.cc
@@ -14,11 +14,13 @@
 #include "base/command_line.h"
 #include "base/compiler_specific.h"
 #include "base/environment.h"
+#include "base/file_util.h"
 #include "base/files/file_path.h"
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/metrics/histogram.h"
+#include "base/metrics/statistics_recorder.h"
 #include "base/path_service.h"
 #include "base/prefs/pref_service.h"
 #include "base/strings/string_number_conversions.h"
@@ -227,6 +229,21 @@ class ProfileLaunchObserver : public content::NotificationObserver {
 base::LazyInstance<ProfileLaunchObserver> profile_launch_observer =
     LAZY_INSTANCE_INITIALIZER;
 
+// This function should only be called in the blocking pool.

[Alexei Svitkine (slow), 2013/11/13 19:04:32]

Nit: Have the comment actually briefly mention what this does.

[grt (UTC plus 2), 2013/11/14 05:08:51]

Done.

+void DumpBrowserHistograms(const base::FilePath& output_file) {
+  base::ThreadRestrictions::AssertIOAllowed();
+
+  if (base::PathExists(output_file))
+    return;
+
+  std::string output_string;
+  base::StatisticsRecorder::WriteJSON(std::string(), &output_string);
+  if (output_string.size() <= INT_MAX) {
+    file_util::WriteFile(output_file, output_string.data(),
+                         static_cast<int>(output_string.size()));
+  }
+}
+
 }  // namespace
 
 StartupBrowserCreator::StartupBrowserCreator()
@@ -602,6 +619,17 @@ bool StartupBrowserCreator::ProcessCmdLineImpl(
   ui::TouchFactory::SetTouchDeviceListFromCommandLine();
 #endif
 
+  if (!process_startup) {

[marja, 2013/11/13 15:37:34]

Doing some code searching, it seems process_startup is also false when we're
creating a new profile and launch it. In that case previously, silent_launch was
not set to true, and now you're setting it to true. That doesn't seem right.

[grt (UTC plus 2), 2013/11/14 05:08:51]

Indeed. Nice catch. I had meant for silent_launch only to be set if the new
switch was present. I've fixed the code and added a comment to this effect.

+    base::FilePath output_file(
+        command_line.GetSwitchValuePath(switches::kDumpBrowserHistograms));
+    if (!output_file.empty()) {
+      BrowserThread::PostBlockingPoolTask(
+          FROM_HERE,
+          base::Bind(&DumpBrowserHistograms, output_file));
+    }
+    silent_launch = true;
+  }
+
   // If we don't want to launch a new browser window or tab (in the case
   // of an automation request), we are done here.
   if (silent_launch)