Store PreRead options obtained from the registry in a global variable.

chrome/app/main_dll_loader_win.cc

Index: chrome/app/main_dll_loader_win.cc
diff --git a/chrome/app/main_dll_loader_win.cc b/chrome/app/main_dll_loader_win.cc
index a70a6787d1504d0f2ce48b52ae09ce9325ac2f9b..c959114371ec3f3dfe7369463c87e4398e1daf21 100644
--- a/chrome/app/main_dll_loader_win.cc
+++ b/chrome/app/main_dll_loader_win.cc
@@ -64,35 +64,34 @@ HMODULE LoadModuleWithDirectory(const base::FilePath& module) {
   ::SetCurrentDirectoryW(module.DirName().value().c_str());
 
   // Get pre-read options from the PreRead field trial.
-  bool trial_no_pre_read = false;
-  bool trial_high_priority = false;
-  bool trial_only_if_cold = false;
-  bool trial_prefetch_virtual_memory = false;
-  startup_metric_utils::GetPreReadOptions(
-      BrowserDistribution::GetDistribution()->GetRegistryPath(),
-      &trial_no_pre_read, &trial_high_priority, &trial_only_if_cold,
-      &trial_prefetch_virtual_memory);
+  startup_metric_utils::InitializePreReadOptions(

[gab, 2016/01/20 20:09:39]

This makes me think that this is/was wrong, later renderers will read the
updated registry value and report being in the group meant for the next
startup...

Since the browser passes field trials to the renderers, here we should probably
inspect existing field trials and use the Synthetic one instead of reading from
registry?

[fdoray, 2016/01/20 21:58:53]

As we discussed, this isn't problematic as long as we don't look at the metrics
of old groups.

+      BrowserDistribution::GetDistribution()->GetRegistryPath());
+  const int pre_read_options = startup_metric_utils::GetPreReadOptions();
 
   // Pre-read the binary to warm the memory caches (avoids a lot of random IO).
-  if (!trial_no_pre_read) {
+  if (!(pre_read_options & startup_metric_utils::PRE_READ_OPTION_NO_PRE_READ)) {
     base::ThreadPriority previous_priority = base::ThreadPriority::NORMAL;
-    if (trial_high_priority) {
+    if (pre_read_options &
+        startup_metric_utils::PRE_READ_OPTION_HIGH_PRIORITY) {
       previous_priority = base::PlatformThread::GetCurrentThreadPriority();
       base::PlatformThread::SetCurrentThreadPriority(
           base::ThreadPriority::DISPLAY);
     }
 
-    if (trial_only_if_cold) {
+    if (pre_read_options & startup_metric_utils::PRE_READ_OPTION_ONLY_IF_COLD) {
       base::MemoryMappedFile module_memory_map;
       const bool map_initialize_success = module_memory_map.Initialize(module);
       DCHECK(map_initialize_success);
       if (!IsMemoryMappedFileWarm(module_memory_map)) {
-        if (trial_prefetch_virtual_memory)
+        if (pre_read_options &
+            startup_metric_utils::PRE_READ_OPTION_PREFETCH_VIRTUAL_MEMORY) {
           PreReadMemoryMappedFile(module_memory_map, module);
-        else
+        } else {
           PreReadFile(module);
+        }
       }
-    } else if (trial_prefetch_virtual_memory) {
+    } else if (pre_read_options &
+               startup_metric_utils::PRE_READ_OPTION_PREFETCH_VIRTUAL_MEMORY) {
       base::MemoryMappedFile module_memory_map;
       const bool map_initialize_success = module_memory_map.Initialize(module);
       DCHECK(map_initialize_success);
@@ -101,7 +100,7 @@ HMODULE LoadModuleWithDirectory(const base::FilePath& module) {
       PreReadFile(module);
     }
 
-    if (trial_high_priority)
+    if (pre_read_options & startup_metric_utils::PRE_READ_OPTION_HIGH_PRIORITY)
       base::PlatformThread::SetCurrentThreadPriority(previous_priority);
   }