Avoid doing periodic prerender cleanup when there are no contents.

chrome/browser/prerender/prerender_field_trial.cc

Index: chrome/browser/prerender/prerender_field_trial.cc
diff --git a/chrome/browser/prerender/prerender_field_trial.cc b/chrome/browser/prerender/prerender_field_trial.cc
index d89a31d77d3bf6a3f1651f67b7c298ec8eca226e..de10c1b336810a5f2a1c4b1b999f212f6cb96ecf 100644
--- a/chrome/browser/prerender/prerender_field_trial.cc
+++ b/chrome/browser/prerender/prerender_field_trial.cc
@@ -90,22 +90,27 @@ void SetupPrerenderFieldTrial() {
   FieldTrial::Probability experiment_multi_prerender_probability;
   FieldTrial::Probability experiment_15min_ttl_probability;
   FieldTrial::Probability experiment_no_use_probability;
+  FieldTrial::Probability experiment_match_complete_probability;
 
   chrome::VersionInfo::Channel channel = chrome::VersionInfo::GetChannel();
   if (channel == chrome::VersionInfo::CHANNEL_STABLE ||
       channel == chrome::VersionInfo::CHANNEL_BETA) {
     // Use very conservatives and stable settings in beta and stable.
-    const FieldTrial::Probability release_prerender_enabled_probability = 980;
+    const FieldTrial::Probability release_prerender_enabled_probability = 970;
     const FieldTrial::Probability release_control_probability = 10;
     const FieldTrial::Probability
         release_experiment_multi_prerender_probability = 0;
     const FieldTrial::Probability release_experiment_15min_ttl_probability = 10;
     const FieldTrial::Probability release_experiment_no_use_probability = 0;
+    const FieldTrial::Probability
+        release_experiment_match_complete_probability = 10;
     COMPILE_ASSERT(
-        release_prerender_enabled_probability + release_control_probability +
+        release_prerender_enabled_probability +
+        release_control_probability +
         release_experiment_multi_prerender_probability +
         release_experiment_15min_ttl_probability +
-        release_experiment_no_use_probability == divisor,
+        release_experiment_no_use_probability +
+        release_experiment_match_complete_probability == divisor,
         release_experiment_probabilities_must_equal_divisor);
 
     control_probability = release_control_probability;
@@ -113,19 +118,25 @@ void SetupPrerenderFieldTrial() {
         release_experiment_multi_prerender_probability;
     experiment_15min_ttl_probability = release_experiment_15min_ttl_probability;
     experiment_no_use_probability = release_experiment_no_use_probability;
+    experiment_match_complete_probability =
+        release_experiment_match_complete_probability;
   } else {
     // In testing channels, use more experiments and a larger control group to
     // improve quality of data.
     const FieldTrial::Probability dev_prerender_enabled_probability = 250;
     const FieldTrial::Probability dev_control_probability = 250;
     const FieldTrial::Probability
-        dev_experiment_multi_prerender_probability = 250;
-    const FieldTrial::Probability dev_experiment_15min_ttl_probability = 125;
-    const FieldTrial::Probability dev_experiment_no_use_probability = 125;
-    COMPILE_ASSERT(dev_prerender_enabled_probability + dev_control_probability +
+        dev_experiment_multi_prerender_probability = 200;

[tonyg, 2014/09/13 01:12:01]

I made these up. PLMK what %ages you'd like.

+    const FieldTrial::Probability dev_experiment_15min_ttl_probability = 100;
+    const FieldTrial::Probability dev_experiment_no_use_probability = 100;
+    const FieldTrial::Probability
+        dev_experiment_match_complete_probability = 100;
+    COMPILE_ASSERT(dev_prerender_enabled_probability +
+                   dev_control_probability +
                    dev_experiment_multi_prerender_probability +
                    dev_experiment_15min_ttl_probability +
-                   dev_experiment_no_use_probability == divisor,
+                   dev_experiment_no_use_probability +
+                   dev_experiment_match_complete_probability == divisor,
                    dev_experiment_probabilities_must_equal_divisor);
 
     control_probability = dev_control_probability;
@@ -133,6 +144,8 @@ void SetupPrerenderFieldTrial() {
         dev_experiment_multi_prerender_probability;
     experiment_15min_ttl_probability = dev_experiment_15min_ttl_probability;
     experiment_no_use_probability = dev_experiment_no_use_probability;
+    experiment_match_complete_probability =
+        dev_experiment_match_complete_probability;
   }
 
   int prerender_enabled_group = -1;
@@ -153,6 +166,9 @@ void SetupPrerenderFieldTrial() {
   const int experiment_no_use_group =
       trial->AppendGroup("PrerenderNoUse",
                          experiment_no_use_probability);
+  const int experiment_match_complete_group =
+      trial->AppendGroup("MatchComplete",
+                         experiment_match_complete_probability);
 
   const int trial_group = trial->group();
   if (trial_group == prerender_enabled_group) {
@@ -170,6 +186,9 @@ void SetupPrerenderFieldTrial() {
   } else if (trial_group == experiment_no_use_group) {
     PrerenderManager::SetMode(
         PrerenderManager::PRERENDER_MODE_EXPERIMENT_NO_USE_GROUP);
+  } else if (trial_group == experiment_match_complete_group) {
+    PrerenderManager::SetMode(
+        PrerenderManager::PRERENDER_MODE_EXPERIMENT_MATCH_COMPLETE_GROUP);
   } else {
     NOTREACHED();
   }