Revert 98319 - Make a channel and time limited persistent PreRead experiment...

chrome/app/client_util.cc

Index: chrome/app/client_util.cc
===================================================================
--- chrome/app/client_util.cc	(revision 98387)
+++ chrome/app/client_util.cc	(working copy)
@@ -11,7 +11,6 @@
 #include "base/file_util.h"
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
-#include "base/rand_util.h"  // For PreRead experiment.
 #include "base/string_util.h"
 #include "base/utf_string_conversions.h"
 #include "base/version.h"
@@ -24,7 +23,6 @@
 #include "chrome/installer/util/browser_distribution.h"
 #include "chrome/installer/util/channel_info.h"
 #include "chrome/installer/util/install_util.h"
-#include "chrome/installer/util/google_chrome_sxs_distribution.h"  // PreRead.
 #include "chrome/installer/util/google_update_constants.h"
 #include "chrome/installer/util/google_update_settings.h"
 #include "chrome/installer/util/util_constants.h"
@@ -85,90 +83,10 @@
   return true;
 }
 
-#if defined(OS_WIN)
-// These constants are used by the PreRead experiment.
-const wchar_t kPreReadRegistryValue[] = L"PreReadExperimentGroup";
-const int kPreReadExpiryYear = 2012;
-const int kPreReadExpiryMonth = 1;
-const int kPreReadExpiryDay = 1;
-
-bool PreReadShouldRun() {
-  base::Time::Exploded exploded = { 0 };
-  exploded.year = kPreReadExpiryYear;
-  exploded.month = kPreReadExpiryMonth;
-  exploded.day_of_month = kPreReadExpiryDay;
-
-  base::Time expiration_time = base::Time::FromLocalExploded(exploded);
-
-  // Get the build time. This code is copied from
-  // base::FieldTrial::GetBuildTime. We can't use MetricsLogBase::GetBuildTime
-  // because that's in seconds since Unix epoch, which base::Time can't use.
-  base::Time build_time;
-  const char* kDateTime = __DATE__ " " __TIME__;
-  bool result = base::Time::FromString(kDateTime, &build_time);
-  DCHECK(result);
-
-  // If the experiment is expired, don't run it.
-  if (build_time > expiration_time)
-    return false;
-
-#if defined(GOOGLE_CHROME_BUILD)
-  // The experiment should only run on canary and dev.
-  BrowserDistribution* dist = BrowserDistribution::GetDistribution();
-  std::wstring channel;
-  if (!dist->GetChromeChannel(&channel))
-    return false;
-  return channel == GoogleChromeSxSDistribution::GetChannel() ||
-      channel == L"dev";
-#else
-  // If we're running Chromium, we have no concept of channel so we
-  // run the experiment.
-  return true;
-#endif
-}
-
-// Checks to see if the experiment is running. If so, either tosses a coin
-// and persists it, or gets the already persistent coin-toss value. Returns
-// the coin-toss via |pre_read|. Returns true if the experiment is running and
-// pre_read has been written, false otherwise. |pre_read| is only written to
-// when this function returns true. |key| must be open with read-write access,
-// and be valid.
-bool GetPreReadExperimentGroup(base::win::RegKey* key,
-                               DWORD* pre_read) {
-  DCHECK(key != NULL);
-  DCHECK(pre_read != NULL);
-
-  if (!PreReadShouldRun()) {
-    // The experiment is no longer running. Remove the registry key
-    // storing the coin toss.
-    key->DeleteValue(kPreReadRegistryValue);
-    return false;
-  }
-
-  // Coin already tossed?
-  DWORD coin_toss = 0;
-  if (key->ReadValueDW(kPreReadRegistryValue, &coin_toss) == ERROR_SUCCESS) {
-    *pre_read = coin_toss;
-    return true;
-  }
-
-  // Coin not tossed? Toss it, and save the value to the registry.
-  coin_toss = base::RandInt(0, 1);
-  DCHECK(coin_toss == 0 || coin_toss == 1);
-  if (key->WriteValue(kPreReadRegistryValue, coin_toss) == ERROR_SUCCESS) {
-    *pre_read = coin_toss;
-    return true;
-  }
-
-  return false;
-}
-#endif  // if defined(OS_WIN)
-
 // Expects that |dir| has a trailing backslash. |dir| is modified so it
 // contains the full path that was tried. Caller must check for the return
 // value not being null to determine if this path contains a valid dll.
-HMODULE LoadChromeWithDirectory(const std::wstring& reg_key,  // For PreRead.
-                                std::wstring* dir) {
+HMODULE LoadChromeWithDirectory(std::wstring* dir) {
   ::SetCurrentDirectoryW(dir->c_str());
   const CommandLine& cmd_line = *CommandLine::ForCurrentProcess();
 #ifdef _WIN64
@@ -220,32 +138,6 @@
       key.Close();
     }
 
-    // The PreRead experiment is unable to use the standard FieldTrial
-    // mechanism as pre-reading happens in chrome.exe prior to loading
-    // chrome.dll. As such, we use a custom approach. If the experiment is
-    // running (not expired, and we're running a version of chrome from an
-    // appropriate channel) then we look to the registry for the experiment
-    // group. If it is not found, we toss a coin and persist the result in the
-    // registry. The coin-toss value is communicated to chrome.dll via an
-    // environment variable, which indicates to chrome.dll that the experiment
-    // is running, causing it to report sub-histogram results. If the experiment
-    // is expired or not running, the registry key is removed.
-
-    base::win::RegKey exp_key(
-        HKEY_CURRENT_USER, reg_key.c_str(),
-        KEY_CREATE_SUB_KEY | KEY_QUERY_VALUE | KEY_SET_VALUE);
-
-    if (exp_key.Valid()) {
-      // If the experiment is running, indicate it to chrome.dll via an
-      // environment variable.
-      if (GetPreReadExperimentGroup(&exp_key, &pre_read)) {
-        scoped_ptr<base::Environment> env(base::Environment::Create());
-        env->SetVar(chrome::kPreReadEnvironmentVariable,
-                    pre_read ? "1" : "0");
-      }
-      exp_key.Close();
-    }
-
     if (pre_read) {
       TRACE_EVENT_BEGIN_ETW("PreReadImage", 0, "");
       file_util::PreReadImage(dir->c_str(), pre_read_size, pre_read_step_size);
@@ -269,7 +161,7 @@
   GoogleUpdateSettings::UpdateDidRunState(false, system_level);
 }
 
-}  // namespace
+}
 //=============================================================================
 
 MainDllLoader::MainDllLoader() : dll_(NULL) {
@@ -291,7 +183,7 @@
 HMODULE MainDllLoader::Load(std::wstring* out_version, std::wstring* out_file) {
   std::wstring dir(GetExecutablePath());
   *out_file = dir;
-  HMODULE dll = LoadChromeWithDirectory(GetRegistryPath(), out_file);
+  HMODULE dll = LoadChromeWithDirectory(out_file);
   if (dll)
     return dll;
 
@@ -330,7 +222,7 @@
     *out_file = dir;
     *out_version = version_string;
     out_file->append(*out_version).append(L"\\");
-    dll = LoadChromeWithDirectory(GetRegistryPath(), out_file);
+    dll = LoadChromeWithDirectory(out_file);
     if (!dll) {
       LOG(ERROR) << "Failed to load Chrome DLL from " << out_file;
     }