Updated about_flags and command-line switch handling for prerender/prefetch

The second half of http://codereview.chromium.org/6410082/ , which
cbentzel suggested be landed in two halves.

This upload addresses comments from that review (improved description,
unified options, no more contradictory option possibilities).

BUG=70610
TEST=lots of manual testing, http://browserspy.dk/prefetch.php

Review URL: http://codereview.chromium.org/6480002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@74740 0039d316-1c4b-4281-b951-d872f2087c98

9 files changed, 117 insertions, 53 deletions

diff --git a/chrome/app/generated_resources.grd b/chrome/app/generated_resources.grd
index c6d88b7..47a3de1 100644
--- a/chrome/app/generated_resources.grd
+++ b/chrome/app/generated_resources.grd
@@ -4050,11 +4050,20 @@ Keep your key file in a safe place. You will need it to create new versions of y
       <message name="IDS_FLAGS_DNS_SERVER_DESCRIPTION" desc="">
         User specified DNS server, which Chrome will use for DNS resolutions rather than the system defaults.
       </message>
-      <message name="IDS_FLAGS_PAGE_PRERENDER_NAME" desc="">
+      <message name="IDS_FLAGS_PAGE_PRERENDER_NAME" desc="Name of the 'Prerendering' lab.">
         Web Page Prerendering.
       </message>
-      <message name="IDS_FLAGS_PAGE_PRERENDER_DESCRIPTION" desc="">
-        Speculatively prerenders complete webpages in the background for a faster browsing experience.
+      <message name="IDS_FLAGS_PAGE_PRERENDER_DESCRIPTION" desc="Description of the 'Prerendering' lab.">
+        Speculatively prerenders complete webpages in the background for a faster browsing experience.  The default setting of automatic can cause this feature to enable/disable randomly for testing purposes.\n
+      </message>
+      <message name="IDS_FLAGS_PAGE_PRERENDER_AUTOMATIC" desc="Option name for automatic selection in the 'Prerendering' lab">
+	Automatic
+      </message>
+      <message name="IDS_FLAGS_PAGE_PRERENDER_ENABLED" desc="Option name for always enabling the 'Prerendering' lab">
+	Always Enabled
+      </message>
+      <message name="IDS_FLAGS_PAGE_PRERENDER_DISABLED" desc="Option name for always disabling the 'Prerendering' lab">
+	Always Disabled
       </message>
       <message name="IDS_FLAGS_CONFIRM_TO_QUIT_NAME" desc="Name of the 'Confirm to Quit' lab.">
         Confirm to Quit
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 9193489..f2374ed 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -28,7 +28,7 @@ namespace about_flags {
 #define SINGLE_VALUE_TYPE(command_line_switch) \
     SINGLE_VALUE_TYPE_AND_VALUE(command_line_switch, "")
 #define MULTI_VALUE_TYPE(choices) \
-    Experiment::MULTI_VALUE, "", choices, arraysize(choices)
+    Experiment::MULTI_VALUE, "", "", choices, arraysize(choices)
 
 namespace {
 
@@ -40,6 +40,14 @@ const char kMediaPlayerExperimentName[] = "media-player";
 const char kAdvancedFileSystemExperimentName[] = "advanced-file-system";
 const char kVerticalTabsExperimentName[] = "vertical-tabs";
 
+const Experiment::Choice kPagePrerenderChoices[] = {
+  { IDS_FLAGS_PAGE_PRERENDER_AUTOMATIC, "", "" },
+  { IDS_FLAGS_PAGE_PRERENDER_ENABLED,
+    switches::kPrerender, switches::kPrerenderSwitchValueEnabled },
+  { IDS_FLAGS_PAGE_PRERENDER_DISABLED,
+    switches::kPrerender, switches::kPrerenderSwitchValueDisabled },
+};
+
 // RECORDING USER METRICS FOR FLAGS:
 // -----------------------------------------------------------------------------
 // The first line of the experiment is the internal name. If you'd like to
@@ -195,7 +203,7 @@ const Experiment kExperiments[] = {
     IDS_FLAGS_PAGE_PRERENDER_NAME,
     IDS_FLAGS_PAGE_PRERENDER_DESCRIPTION,
     kOsAll,
-    SINGLE_VALUE_TYPE(switches::kEnablePagePrerender)
+    MULTI_VALUE_TYPE(kPagePrerenderChoices)
   },
   {
     "confirm-to-quit",  // FLAGS:RECORD_UMA
diff --git a/chrome/browser/browser_main.cc b/chrome/browser/browser_main.cc
index b813a17..9ef2054 100644
--- a/chrome/browser/browser_main.cc
+++ b/chrome/browser/browser_main.cc
@@ -429,39 +429,76 @@ void BrowserMainParts::SpdyFieldTrial() {
   }
 }
 
-// If any of --enable-prerender, --enable-content-prefetch or
-// --disable-content-prefetch are set, use those to determine if
-// prefetch is enabled. Otherwise, randomly assign users to an A/B test for
-// prefetching.
+// Parse the --prerender= command line switch, which controls both prerendering
+// and prefetching.  If the switch is unset, or is set to "auto", then the user
+// is assigned to a field trial.
 void BrowserMainParts::PrefetchAndPrerenderFieldTrial() {
-  if (parsed_command_line().HasSwitch(switches::kEnableContentPrefetch) ||
-      parsed_command_line().HasSwitch(switches::kEnablePagePrerender))
-    ResourceDispatcherHost::set_is_prefetch_enabled(true);
-  else if (parsed_command_line().HasSwitch(switches::kDisableContentPrefetch)) {
-    ResourceDispatcherHost::set_is_prefetch_enabled(false);
-  } else {
-    const base::FieldTrial::Probability kPrefetchDivisor = 1000;
-    const base::FieldTrial::Probability no_prefetch_probability = 500;
-    // After June 30, 2011 builds, it will always be in default group.
-    scoped_refptr<base::FieldTrial> trial(
-        new base::FieldTrial("Prefetch", kPrefetchDivisor,
-            "ContentPrefetchEnabled", 2011, 6, 30));
-    const int yes_prefetch_grp = trial->kDefaultGroupNumber;
-    trial->AppendGroup("ContentPrefetchDisabled", no_prefetch_probability);
-    const int trial_grp = trial->group();
-    ResourceDispatcherHost::set_is_prefetch_enabled(
-        trial_grp == yes_prefetch_grp);
+  enum PrerenderOption {
+    PRERENDER_OPTION_AUTO,
+    PRERENDER_OPTION_DISABLED,
+    PRERENDER_OPTION_ENABLED,
+    PRERENDER_OPTION_PREFETCH_ONLY,
+  };
+
+  PrerenderOption prerender_option = PRERENDER_OPTION_AUTO;
+  if (parsed_command_line().HasSwitch(switches::kPrerender)) {
+    const std::string switch_value =
+        parsed_command_line().GetSwitchValueASCII(switches::kPrerender);
+
+    if (switch_value == switches::kPrerenderSwitchValueAuto) {
+      prerender_option = PRERENDER_OPTION_AUTO;
+    } else if (switch_value == switches::kPrerenderSwitchValueDisabled) {
+      prerender_option = PRERENDER_OPTION_DISABLED;
+    } else if (switch_value.empty() ||
+               switch_value == switches::kPrerenderSwitchValueEnabled) {
+      // The empty string means the option was provided with no value, and that
+      // means enable.
+      prerender_option = PRERENDER_OPTION_ENABLED;
+    } else if (switch_value == switches::kPrerenderSwitchValuePrefetchOnly) {
+      prerender_option = PRERENDER_OPTION_PREFETCH_ONLY;
+    } else {
+      prerender_option = PRERENDER_OPTION_DISABLED;
+      LOG(ERROR) << "Invalid --prerender option received on command line: "
+                 << switch_value;
+      LOG(ERROR) << "Disabling prerendering!";
+    }
   }
 
-  PrerenderManager::PrerenderManagerMode prerender_mode =
-      PrerenderManager::PRERENDER_MODE_DISABLED;
-  if (parsed_command_line().HasSwitch(switches::kEnablePagePrerender))
-    prerender_mode = PrerenderManager::PRERENDER_MODE_ENABLED;
-  else
-    prerender_mode = PrerenderManager::PRERENDER_MODE_DISABLED;
-  PrerenderManager::SetMode(prerender_mode);
+  switch (prerender_option) {
+    case PRERENDER_OPTION_AUTO: {
+      const base::FieldTrial::Probability kPrefetchDivisor = 1000;
+      const base::FieldTrial::Probability no_prefetch_probability = 500;
+      // After June 30, 2011 builds, it will always be in default group.
+      scoped_refptr<base::FieldTrial> trial(
+          new base::FieldTrial("Prefetch", kPrefetchDivisor,
+                               "ContentPrefetchEnabled", 2011, 6, 30));
+      const int yes_prefetch_grp = trial->kDefaultGroupNumber;
+      trial->AppendGroup("ContentPrefetchDisabled", no_prefetch_probability);
+      const int trial_grp = trial->group();
+      ResourceDispatcherHost::set_is_prefetch_enabled(
+          trial_grp == yes_prefetch_grp);
+
+      // There is currently no prerendering field trial.
+      PrerenderManager::SetMode(PrerenderManager::PRERENDER_MODE_DISABLED);
+      break;
+    }
+    case PRERENDER_OPTION_DISABLED:
+      ResourceDispatcherHost::set_is_prefetch_enabled(false);
+      PrerenderManager::SetMode(PrerenderManager::PRERENDER_MODE_DISABLED);
+      break;
+    case PRERENDER_OPTION_ENABLED:
+      ResourceDispatcherHost::set_is_prefetch_enabled(true);
+      PrerenderManager::SetMode(PrerenderManager::PRERENDER_MODE_ENABLED);
+      break;
+    case PRERENDER_OPTION_PREFETCH_ONLY:
+      ResourceDispatcherHost::set_is_prefetch_enabled(true);
+      PrerenderManager::SetMode(PrerenderManager::PRERENDER_MODE_DISABLED);
+      break;
+    default:
+      NOTREACHED();
+  }
 
-  UMA_HISTOGRAM_ENUMERATION("Prerender.Sessions", prerender_mode,
+  UMA_HISTOGRAM_ENUMERATION("Prerender.Sessions", PrerenderManager::GetMode(),
                             PrerenderManager::PRERENDER_MODE_MAX);
 }
 
diff --git a/chrome/browser/prerender/prerender_browsertest.cc b/chrome/browser/prerender/prerender_browsertest.cc
index 116a6d7..c31817e 100644
--- a/chrome/browser/prerender/prerender_browsertest.cc
+++ b/chrome/browser/prerender/prerender_browsertest.cc
@@ -92,7 +92,8 @@ class PrerenderBrowserTest : public InProcessBrowserTest {
   }
 
   virtual void SetUpCommandLine(CommandLine* command_line) {
-    command_line->AppendSwitch(switches::kEnablePagePrerender);
+    command_line->AppendSwitchASCII(switches::kPrerender,
+                                    switches::kPrerenderSwitchValueEnabled);
 #if defined(OS_MACOSX)
     // The plugins directory isn't read by default on the Mac, so it needs to be
     // explicitly registered.
diff --git a/chrome/browser/prerender/prerender_manager.cc b/chrome/browser/prerender/prerender_manager.cc
index e4f4508..6e28a2c 100644
--- a/chrome/browser/prerender/prerender_manager.cc
+++ b/chrome/browser/prerender/prerender_manager.cc
@@ -33,6 +33,13 @@ void PrerenderManager::SetMode(PrerenderManagerMode mode) {
   mode_ = mode;
 }
 
+// static
+bool PrerenderManager::IsPrerenderingEnabled() {
+  return
+      GetMode() == PRERENDER_MODE_ENABLED ||
+      GetMode() == PRERENDER_MODE_EXPERIMENT_PRERENDER_GROUP;
+}
+
 struct PrerenderManager::PrerenderContentsData {
   PrerenderContents* contents_;
   base::Time start_time_;
diff --git a/chrome/browser/prerender/prerender_manager.h b/chrome/browser/prerender/prerender_manager.h
index de54500..6a62915 100644
--- a/chrome/browser/prerender/prerender_manager.h
+++ b/chrome/browser/prerender/prerender_manager.h
@@ -66,6 +66,7 @@ class PrerenderManager : public base::RefCounted<PrerenderManager> {
 
   static PrerenderManagerMode GetMode();
   static void SetMode(PrerenderManagerMode mode);
+  static bool IsPrerenderingEnabled();
 
   // The following static method can be called from any thread, but will result
   // in posting a task to the UI thread if we are not in the UI thread.
diff --git a/chrome/browser/profiles/profile_impl.cc b/chrome/browser/profiles/profile_impl.cc
index 8cc2ec7..c585ebc 100644
--- a/chrome/browser/profiles/profile_impl.cc
+++ b/chrome/browser/profiles/profile_impl.cc
@@ -1500,8 +1500,7 @@ PrefProxyConfigTracker* ProfileImpl::GetProxyConfigTracker() {
 }
 
 PrerenderManager* ProfileImpl::GetPrerenderManager() {
-  CommandLine* cl = CommandLine::ForCurrentProcess();
-  if (!cl->HasSwitch(switches::kEnablePagePrerender))
+  if (!PrerenderManager::IsPrerenderingEnabled())
     return NULL;
   if (!prerender_manager_)
     prerender_manager_ = new PrerenderManager(this);
diff --git a/chrome/common/chrome_switches.cc b/chrome/common/chrome_switches.cc
index a53c979..182e9c9 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -208,11 +208,6 @@ const char kDisableBlockContentAnimation[]  =
 // exceeded.
 const char kDisableConnectBackupJobs[]      = "disable-connect-backup-jobs";
 
-// Disable requests that webkit labels TargetIsPrefetch.  As of
-// writing only <link rel=prefetch...> but also eventually
-// Link: headers.
-const char kDisableContentPrefetch[]        = "disable-content-prefetch";
-
 // Disables the custom JumpList on Windows 7.
 const char kDisableCustomJumpList[]         = "disable-custom-jumplist";
 
@@ -480,11 +475,6 @@ const char kEnableConfirmToQuit[]           = "enable-confirm-to-quit";
 // exceeded.
 const char kEnableConnectBackupJobs[]       = "enable-connect-backup-jobs";
 
-// Enable requests that webkit labels TargetIsPrefetch.  As of
-// writing only <link rel=prefetch...> but also eventually
-// Link: headers.
-const char kEnableContentPrefetch[]         = "enable-content-prefetch";
-
 // Enables web developers to create apps for Chrome without using crx packages.
 const char kEnableCrxlessWebApps[]          = "enable-crxless-web-apps";
 
@@ -562,9 +552,6 @@ const char kEnableRemoting[]                = "enable-remoting";
 const char kEnableResourceContentSettings[] =
     "enable-resource-content-settings";
 
-// Enable speculative prerendering of pages.
-const char kEnablePagePrerender[]           = "enable-page-prerender";
-
 // Enable speculative TCP/IP preconnection.
 const char kEnablePreconnect[]              = "enable-preconnect";
 
@@ -944,6 +931,19 @@ const char kPpapiPluginProcess[]            = "ppapi";
 // Causes the PPAPI sub process to display a dialog on launch.
 const char kPpapiStartupDialog[]            = "ppapi-startup-dialog";
 
+// Controls speculative prerendering of pages, and content prefetching.  Both
+// are dispatched from <link rel=prefetch href=...> elements.
+const char kPrerender[]                     = "prerender";
+// These are the values the switch may have, as in "--prerender=auto".
+//   auto: Allow field trial selection in both prerender and prefetch.
+const char kPrerenderSwitchValueAuto[]      = "auto";
+//   disabled: No prerendering or prefetching.
+const char kPrerenderSwitchValueDisabled[]  = "disabled";
+//   enabled: Both prerendering and prefetching.
+const char kPrerenderSwitchValueEnabled[]   = "enabled";
+//   prefetch_only: No prerendering, but enable prefetching.
+const char kPrerenderSwitchValuePrefetchOnly[] = "prefetch_only";
+
 // Prints the pages on the screen.
 const char kPrint[]                         = "print";
 
diff --git a/chrome/common/chrome_switches.h b/chrome/common/chrome_switches.h
index b2504e0..d18661f 100644
--- a/chrome/common/chrome_switches.h
+++ b/chrome/common/chrome_switches.h
@@ -67,7 +67,6 @@ extern const char kDisableBackgroundNetworking[];
 extern const char kDisableBackingStoreLimit[];
 extern const char kDisableBlockContentAnimation[];
 extern const char kDisableConnectBackupJobs[];
-extern const char kDisableContentPrefetch[];
 extern const char kDisableCustomJumpList[];
 extern const char kDisableDatabases[];
 extern const char kDisableDesktopNotifications[];
@@ -143,7 +142,6 @@ extern const char kEnableCloudPrintProxy[];
 extern const char kEnableCloudPrint[];
 extern const char kEnableConfirmToQuit[];
 extern const char kEnableConnectBackupJobs[];
-extern const char kEnableContentPrefetch[];
 extern const char kEnableCrxlessWebApps[];
 extern const char kEnableDeviceMotion[];
 extern const char kEnableDNSCertProvenanceChecking[];
@@ -163,7 +161,6 @@ extern const char kEnableMonitorProfile[];
 extern const char kEnableNaCl[];
 extern const char kEnableNaClDebug[];
 extern const char kEnableNativeWebWorkers[];
-extern const char kEnablePagePrerender[];
 extern const char kEnablePreconnect[];
 extern const char kEnablePreparsedJsCaching[];
 extern const char kEnablePrintPreview[];
@@ -270,6 +267,11 @@ extern const char kPpapiOutOfProcess[];
 extern const char kPpapiPluginLauncher[];
 extern const char kPpapiPluginProcess[];
 extern const char kPpapiStartupDialog[];
+extern const char kPrerender[];
+extern const char kPrerenderSwitchValueAuto[];
+extern const char kPrerenderSwitchValueDisabled[];
+extern const char kPrerenderSwitchValueEnabled[];
+extern const char kPrerenderSwitchValuePrefetchOnly[];
 extern const char kPrint[];
 extern const char kProcessPerSite[];
 extern const char kProcessPerTab[];