Optimize ShouldLaunchIncognito() since its on the startup path.

chrome/browser/prefs/incognito_mode_prefs.h

Index: chrome/browser/prefs/incognito_mode_prefs.h
diff --git a/chrome/browser/prefs/incognito_mode_prefs.h b/chrome/browser/prefs/incognito_mode_prefs.h
index cbf30efa6abab726cdf420f57516228d7e370bda..2d02e089ec2d0f32518950916fca938c20907416 100644
--- a/chrome/browser/prefs/incognito_mode_prefs.h
+++ b/chrome/browser/prefs/incognito_mode_prefs.h
@@ -78,6 +78,18 @@ class IncognitoModePrefs {
   static bool ArePlatformParentalControlsEnabled() WARN_UNUSED_RESULT;
 
  private:
+  // Specifies whether parental controls should be checked. See comment below.
+  enum GetAvailabilityMode {

[gab, 2016/10/03 17:08:12]

enum class

[Alexei Svitkine (slow), 2016/10/03 18:57:39]

This requires prefixing all uses of the constants with the name of the enum,
which makes them extremely long - since the constants are already wordy. So I'd
rather keep as-is.

In other cases, the extra prefixing is nice because it makes sure you don't get
conflicts and it's obvious where they're coming from - but since this is a
private constant I don't think the benefits outweigh the extra readability hit
from prefixing and re-wrapping a lot of the code - such as the one in
ShouldLaunchIncognito().

Let me know if you feel strongly about this, though.

[gab, 2016/10/03 19:05:57]

IMO that means that GetAvailabilityMode is too generic of a name. I like a
descriptive enum class name with short options, e.g.:

enum class ConsiderParentalControls {
  YES,
  NO,
};

I find enum class should always be used when the numerical values don't mean
anything.

[Alexei Svitkine (slow), 2016/10/03 19:25:36]

At first I really like this suggestion, but then I realized we'd have to rename
the param to be something like consider_parental_controls instead of mode, which
still makes the code very verbose. :\

Gab and I try to come up with a few different names but couldn't find something
we both liked and was not verbose. So I think we've decided to just keep the
enums.

+    CHECK_PARENTAL_CONTROLS,
+    DONT_CHECK_PARENTAL_CONTROLS,
+  };
+
+  // Internal version of GetAvailability() that specifies whether parental
+  // controls should be checked (which is expensive and not always necessary
+  // to do - such as when checking for FORCED state).
+  static Availability GetAvailabilityInternal(const PrefService* pref_service,
+                                              GetAvailabilityMode mode);
+
   DISALLOW_IMPLICIT_CONSTRUCTORS(IncognitoModePrefs);
 };