Use a valid /prefetch argument when launching a process.

components/startup_metric_utils/common/pre_read_field_trial_utils_win.cc

Index: components/startup_metric_utils/common/pre_read_field_trial_utils_win.cc
diff --git a/components/startup_metric_utils/common/pre_read_field_trial_utils_win.cc b/components/startup_metric_utils/common/pre_read_field_trial_utils_win.cc
index a75a81c6bbef30ca309d63848d86af3fdd45fdb8..65f0eb0677eec577cc5eeaa416bb2c20a90712cc 100644
--- a/components/startup_metric_utils/common/pre_read_field_trial_utils_win.cc
+++ b/components/startup_metric_utils/common/pre_read_field_trial_utils_win.cc
@@ -31,6 +31,7 @@ const base::char16 kHighPriorityVariationName[] = L"HighPriority";
 const base::char16 kOnlyIfColdVariationName[] = L"OnlyIfCold";
 const base::char16 kPrefetchVirtualMemoryVariationName[] =
     L"PrefetchVirtualMemory";
+const base::char16 kNoPrefetchArgumentVariationName[] = L"NoPrefetchArgument";

[gab, 2016/01/26 21:40:26]

It may not be clear to a reader that the reason some of those are "negative" is
that they all change the default, i.e. the default is the inverse of the
variation and thus variations that cancel something we do by default are
negative.

How about describing this in the meta comment for these variable names?

[fdoray, 2016/01/27 20:12:19]

Done.

 
 // Registry key in which the PreRead field trial group is stored.
 const base::char16 kPreReadFieldTrialRegistryKey[] = L"\\PreReadFieldTrial";
@@ -45,6 +46,12 @@ base::string16 GetPreReadRegistryPath(
   return product_registry_path + kPreReadFieldTrialRegistryKey;
 }
 
+// Returns true if |key| has a value named |name| which is not zero.
+bool ReadBool(const base::win::RegKey& key, const base::char16* name) {
+  DWORD value = 0;
+  return key.ReadValueDW(name, &value) == ERROR_SUCCESS && value != 0;
+}
+
 }  // namespace
 
 void InitializePreReadOptions(const base::string16& product_registry_path) {
@@ -57,27 +64,13 @@ void InitializePreReadOptions(const base::string16& product_registry_path) {
                               KEY_QUERY_VALUE);
 
   // Set the PreRead field trial's options.
-  struct {
-    const base::char16* name;
-    bool* option;
-  } const variations_mappings[] = {
-      {kNoPreReadVariationName, &g_pre_read_options.no_pre_read},
-      {kHighPriorityVariationName, &g_pre_read_options.high_priority},
-      {kOnlyIfColdVariationName, &g_pre_read_options.only_if_cold},
-      {kPrefetchVirtualMemoryVariationName,
-       &g_pre_read_options.prefetch_virtual_memory},
-  };
-
-  for (const auto& mapping : variations_mappings) {
-    // Set the option variable to true if the corresponding value is found in
-    // the registry. Set to false otherwise (default behavior).
-    DWORD value = 0;
-    if (key.ReadValueDW(mapping.name, &value) == ERROR_SUCCESS) {
-      DCHECK_EQ(1U, value);
-      DCHECK(!*mapping.option);
-      *mapping.option = true;
-    }
-  }
+  g_pre_read_options.pre_read = !ReadBool(key, kNoPreReadVariationName);
+  g_pre_read_options.high_priority = ReadBool(key, kHighPriorityVariationName);
+  g_pre_read_options.only_if_cold = ReadBool(key, kOnlyIfColdVariationName);
+  g_pre_read_options.prefetch_virtual_memory =
+      ReadBool(key, kPrefetchVirtualMemoryVariationName);
+  g_pre_read_options.prefetch_argument =
+      !ReadBool(key, kNoPrefetchArgumentVariationName);
 }
 
 PreReadOptions GetPreReadOptions() {