Installer support for Windows 10 inactive user toast.

chrome/installer/util/experiment_storage.h

Index: chrome/installer/util/experiment_storage.h
diff --git a/chrome/installer/util/experiment_storage.h b/chrome/installer/util/experiment_storage.h
index 40ed1d2ef170780d915b561e4b4f920212bf0cbd..f7f8c1d4e4e62d0800363ddce7ec71d53928289f 100644
--- a/chrome/installer/util/experiment_storage.h
+++ b/chrome/installer/util/experiment_storage.h
@@ -18,9 +18,9 @@ struct ExperimentMetrics;
 
 // Manages the storage of experiment state on the machine.
 //
-// Participation is a per-install property evaluated one time to determine
-// whether or not the install as a whole participates in the study. It is
-// stored in the install's ClientState key.
+// Participation is a per-install property evaluated one time to determine which
+// study the client participates in. It is stored in the install's ClientState
+// key.
 //
 // ExperimentMetrics are stored in a per-install experiment_label, while the
 // fine-grained Experiment data are stored in a per-user key in Chrome's
@@ -38,16 +38,13 @@ struct ExperimentMetrics;
 // mutex is used for all reads and writes to ensure consistent state.
 class ExperimentStorage {
  public:
-  enum class Participation {
-    // No participation state was found for the install.
-    kNotEvaluated,
+  // An identifier of which study the install participates in.
+  using Study = uint32_t;
 
-    // The client is not participating in the study.
-    kNotParticipating,
-
-    // The client is participating in the study.
-    kIsParticipating,
-  };
+  // The possible Study values.
+  static constexpr Study kNoStudySelected = 0;
+  static constexpr Study kStudyOne = 1;
+  static constexpr Study kStudyTwo = 2;

[Nico, 2017/06/15 14:47:37]

nit: fwiw enum is kind of preferable over static constexpr members because for
static constexpr members you technically need to define storage in the cc, else
you have UB (in practice, this means you'll get a link error if someone takes
the address of the constant -- while with an enum you get a compile error
instead if someone does this). So the lhs version here is imho better -- no UB
and whatnot. (you could just use an enum instead of an enum class of course)

[grt (UTC plus 2), 2017/06/15 15:07:26]

Hmm. Makes sense. I think I made the switch because I didn't want to deal with
casting, but it seems to work just fine as a non-class enum. Thanks.

 
   // Grants the holder exclusive access to the data in the registry. Consumers
   // are expected to not hold an instance across any blocking operations.
@@ -56,12 +53,13 @@ class ExperimentStorage {
     ~Lock();
 
     // Reads the participation state for the install. Returns false in case of
-    // error.
-    bool ReadParticipation(Participation* participation);
+    // error. |participation| is set to kNotEvaluated if no value is present;
+    // otherwise, it is set to the value found.
+    bool ReadParticipation(Study* participation);
 
     // Writes the participation state for the install. Returns false if the
     // write failed.
-    bool WriteParticipation(Participation participation);
+    bool WriteParticipation(Study participation);
 
     // Loads the experiment metrics and data from the registry. Returns false if
     // the state in the registry corresponds to a different user or could not be