Make "source" a required argument of AppLaunchParams and fill in the argument in all call points.

extensions/common/constants.h

Index: extensions/common/constants.h
diff --git a/extensions/common/constants.h b/extensions/common/constants.h
index 25d0be23f9f2880e50f2b1fc1f09ab410400a2d5..34f52c1a002b4473e430cf01a26ae9f3cfb54ba4 100644
--- a/extensions/common/constants.h
+++ b/extensions/common/constants.h
@@ -112,7 +112,7 @@ extern const char kWebStoreAppId[];
 // Note the enumeration is used in UMA histogram so entries
 // should not be re-ordered or removed.
 enum AppLaunchSource {
-  SOURCE_UNTRACKED = 0,
+  SOURCE_UNTRACKED = 0,  // Should be used in test.
   SOURCE_APP_LAUNCHER,
   SOURCE_NEW_TAB_PAGE,
   SOURCE_RELOAD,
@@ -121,10 +121,15 @@ enum AppLaunchSource {
   SOURCE_COMMAND_LINE,
   SOURCE_FILE_HANDLER,
   SOURCE_URL_HANDLER,
-
   SOURCE_SYSTEM_TRAY,
   SOURCE_ABOUT_PAGE,
   SOURCE_KEYBOARD,
+  SOURCE_EXTENSIONS_PAGE,
+  SOURCE_MANAGEMENT_API,
+  SOURCE_EPHEMERAL_APP,
+  SOURCE_BACKGROUND,
+  SOURCE_KIOSK,
+  SOURCE_CHROME_INTERNAL,
 
   NUM_APP_LAUNCH_SOURCES
 };