Add metrics for app banner preventDefault() and prompt().

chrome/browser/banners/app_banner_metrics.h

Index: chrome/browser/banners/app_banner_metrics.h
diff --git a/chrome/browser/banners/app_banner_metrics.h b/chrome/browser/banners/app_banner_metrics.h
index 8b96d8c857f1fb3d0732f1af92d6b55840622c6e..0c04f84959aefecc77fa71aabe71db9e8be338c8 100644
--- a/chrome/browser/banners/app_banner_metrics.h
+++ b/chrome/browser/banners/app_banner_metrics.h
@@ -57,17 +57,30 @@ enum UserResponse {
   USER_RESPONSE_MAX = 7,
 };
 
+enum BeforeInstallEvent {

[Ilya Sherman, 2016/07/06 23:15:53]

nit: Please document that this enum is used to back an UMA histogram, and should
therefore be treated as append-only.

[dominickn, 2016/07/07 00:16:02]

Done.

+  BEFORE_INSTALL_EVENT_MIN = 0,

[Ilya Sherman, 2016/07/06 23:15:53]

Hmm, why are you reserving this bucket?  It doesn't appear to be used.

[dominickn, 2016/07/07 00:16:02]

It's mainly for consistency with the remainder of the histogram enums in this
file. :)

+  BEFORE_INSTALL_EVENT_CREATED = 1,
+  BEFORE_INSTALL_EVENT_COMPLETE = 2,
+  BEFORE_INSTALL_EVENT_NO_ACTION = 3,
+  BEFORE_INSTALL_EVENT_PREVENT_DEFAULT_CALLED = 4,
+  BEFORE_INSTALL_EVENT_PROMPT_CALLED_AFTER_PREVENT_DEFAULT = 5,
+  BEFORE_INSTALL_EVENT_PROMPT_NOT_CALLED_AFTER_PREVENT_DEFAULT = 6,
+  BEFORE_INSTALL_EVENT_MAX = 7,
+};
+
 extern const char kDismissEventHistogram[];
 extern const char kDisplayEventHistogram[];
 extern const char kInstallEventHistogram[];
 extern const char kMinutesHistogram[];
 extern const char kUserResponseHistogram[];
+extern const char kBeforeInstallEventHistogram[];
 
 void TrackDismissEvent(int event);
 void TrackDisplayEvent(int event);
 void TrackInstallEvent(int event);
 void TrackMinutesFromFirstVisitToBannerShown(int minutes);
 void TrackUserResponse(int event);
+void TrackBeforeInstallEvent(int event);
 
 };  // namespace banners