Add "light speed" experiment code for SafeBrowsing service.

chrome/browser/safe_browsing/database_manager.cc

Index: chrome/browser/safe_browsing/database_manager.cc
diff --git a/chrome/browser/safe_browsing/database_manager.cc b/chrome/browser/safe_browsing/database_manager.cc
index 2f89931e50aebce92e15a1c38d6b39a257741cfc..afc3da03f816301b695ebc84a46d9df58a9ff562 100644
--- a/chrome/browser/safe_browsing/database_manager.cc
+++ b/chrome/browser/safe_browsing/database_manager.cc
@@ -30,6 +30,7 @@
 #include "chrome/common/chrome_switches.h"
 #include "components/metrics/metrics_service.h"
 #include "components/startup_metric_utils/startup_metric_utils.h"
+#include "components/variations/variations_associated_data.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/notification_service.h"
 #include "url/url_constants.h"
@@ -167,6 +168,15 @@ SBThreatType GetThreatTypeFromListType(safe_browsing_util::ListType list_type) {
   }
 }
 
+// TODO(asvitkine): Experimental code for measuring start up impact of SB.
+// Remove when experimentation is complete. http://crbug.com/450037
+bool ShouldDisableSafeBrowsing() {
+  DCHECK_CURRENTLY_ON(BrowserThread::IO);
+  static bool disable_sb =
+      !variations::GetVariationParamValue("LightSpeed", "DisableSB").empty();

[gab, 2015/02/13 22:58:21]

Hmmm actually, isn't this boolean logic backwards? i.e. either this bool should
be named |enable_sb| or their shouldn't be a '!'?

I think you want to drop the '!' and keep the rest.

[gab, 2015/02/13 23:00:09]

Oh nvm, it's !empty(), i.e. disabled == not not disabled...! Or enabled = not
not not disabled :-)!

Ugh..!

[gab, 2015/02/13 23:01:36]

Would be nice to have a boolean method on that API rather than have to check
!empty(), just saying :-)!

+  return disable_sb;
+}
+
 }  // namespace
 
 // static
@@ -593,6 +603,10 @@ void SafeBrowsingDatabaseManager::HandleGetHashResults(
 
 void SafeBrowsingDatabaseManager::GetChunks(GetChunksCallback callback) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
+
+  if (ShouldDisableSafeBrowsing())
+    return;
+
   DCHECK(enabled_);
   DCHECK(!callback.is_null());
   safe_browsing_thread_->message_loop()->PostTask(FROM_HERE, base::Bind(
@@ -604,6 +618,10 @@ void SafeBrowsingDatabaseManager::AddChunks(
     scoped_ptr<ScopedVector<SBChunkData> > chunks,
     AddChunksCallback callback) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
+
+  if (ShouldDisableSafeBrowsing())
+    return;
+
   DCHECK(enabled_);
   DCHECK(!callback.is_null());
   safe_browsing_thread_->message_loop()->PostTask(FROM_HERE, base::Bind(
@@ -614,6 +632,10 @@ void SafeBrowsingDatabaseManager::AddChunks(
 void SafeBrowsingDatabaseManager::DeleteChunks(
     scoped_ptr<std::vector<SBChunkDelete> > chunk_deletes) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
+
+  if (ShouldDisableSafeBrowsing())
+    return;
+
   DCHECK(enabled_);
   safe_browsing_thread_->message_loop()->PostTask(FROM_HERE, base::Bind(
       &SafeBrowsingDatabaseManager::DeleteDatabaseChunks, this,
@@ -622,6 +644,10 @@ void SafeBrowsingDatabaseManager::DeleteChunks(
 
 void SafeBrowsingDatabaseManager::UpdateStarted() {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
+
+  if (ShouldDisableSafeBrowsing())
+    return;
+
   DCHECK(enabled_);
   DCHECK(!update_in_progress_);
   update_in_progress_ = true;
@@ -650,6 +676,9 @@ void SafeBrowsingDatabaseManager::StartOnIOThread() {
   if (enabled_)
     return;
 
+  if (ShouldDisableSafeBrowsing())
+    return;
+
   DCHECK(!safe_browsing_thread_.get());
   safe_browsing_thread_.reset(new base::Thread("Chrome_SafeBrowsingThread"));
   if (!safe_browsing_thread_->Start())