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

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 6aa82a19d93e59d8da9f80ca767206fe5f438be6..0219f12d3a6b1acfb09dbccc3d58028b46cd4804 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
@@ -35,6 +35,10 @@ const base::char16 kPrefetchVirtualMemoryVariationName[] =
 // Registry key in which the PreRead field trial group is stored.
 const base::char16 kPreReadFieldTrialRegistryKey[] = L"\\PreReadFieldTrial";
 
+// Pre-read options to use for the current process. This is initialized by
+// InitializePreReadOptions().
+int g_pre_read_options = PRE_READ_OPTION_UNINITIALIZED;

[grt (UTC plus 2), 2016/01/21 04:24:00]

if i'm reading the build files correctly, this .cc file is linked into both
chrome.exe and chrome.dll. there will be one instance of this global variable in
the process for each of these two, so InitializePreReadOptions will need to be
called once from within each module. how will this be done?

[fdoray, 2016/01/21 16:04:16]

Yes. The call in chrome.exe is added by this CL here [1]. The call in chrome.dll
will be added by another CL [2].

[1]
https://codereview.chromium.org/1610733002/diff/60001/chrome/app/main_dll_loa...
[2]
https://codereview.chromium.org/1612663002/diff/1/chrome/browser/chrome_brows...

+
 // Returns the registry path in which the PreRead group is stored.
 base::string16 GetPreReadRegistryPath(
     const base::string16& product_registry_path) {
@@ -43,16 +47,11 @@ base::string16 GetPreReadRegistryPath(
 
 }  // namespace
 
-void GetPreReadOptions(const base::string16& product_registry_path,
-                       bool* no_pre_read,
-                       bool* high_priority,
-                       bool* only_if_cold,
-                       bool* prefetch_virtual_memory) {
+void InitializePreReadOptions(const base::string16& product_registry_path) {
   DCHECK(!product_registry_path.empty());
-  DCHECK(no_pre_read);
-  DCHECK(high_priority);
-  DCHECK(only_if_cold);
-  DCHECK(prefetch_virtual_memory);
+  DCHECK_EQ(g_pre_read_options, PRE_READ_OPTION_UNINITIALIZED);

[grt (UTC plus 2), 2016/01/21 04:24:00]

nit: always put the expected value first when using DCHECK_{EQ,NE} for
consistency with Google Test's {EXPECT,ASSERT}_EQ macro, which requires it.

[fdoray, 2016/01/21 16:04:16]

Done (I removed this line).

+
+  g_pre_read_options = 0;
 
   // Open the PreRead field trial's registry key.
   const base::string16 registry_path =
@@ -63,23 +62,30 @@ void GetPreReadOptions(const base::string16& product_registry_path,
   // Set the PreRead field trial's options.
   struct VariationMapping {

[grt (UTC plus 2), 2016/01/21 04:24:00]

nit: make this an anonymous struct since the name is unused

[fdoray, 2016/01/21 16:04:16]

Done.

     const base::char16* name;
-    bool* variable;
+    PreReadOptions bit;
   } const variations_mappings[] = {
-      {kNoPreReadVariationName, no_pre_read},
-      {kHighPriorityVariationName, high_priority},
-      {kOnlyIfColdVariationName, only_if_cold},
-      {kPrefetchVirtualMemoryVariationName, prefetch_virtual_memory},
+      {kNoPreReadVariationName, PRE_READ_OPTION_NO_PRE_READ},
+      {kHighPriorityVariationName, PRE_READ_OPTION_HIGH_PRIORITY},
+      {kOnlyIfColdVariationName, PRE_READ_OPTION_ONLY_IF_COLD},
+      {kPrefetchVirtualMemoryVariationName,
+       PRE_READ_OPTION_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;
-    *mapping.variable = key.ReadValueDW(mapping.name, &value) == ERROR_SUCCESS;
-    DCHECK(!*mapping.variable || value == 1);
+    if (key.ReadValueDW(mapping.name, &value) == ERROR_SUCCESS) {
+      DCHECK_EQ(1U, value);
+      g_pre_read_options &= mapping.bit;

[grt (UTC plus 2), 2016/01/21 04:24:00]

|=

[fdoray, 2016/01/21 16:04:16]

Done (now using a struct).

+    }
   }
 }
 
+int GetPreReadOptions() {
+  return g_pre_read_options;
+}
+
 void UpdatePreReadOptions(const base::string16& product_registry_path) {
   DCHECK(!product_registry_path.empty());