Add a new field "source" in launchData of chrome.app.runtime.onLaunched() to trace launch source.

extensions/common/switches.cc

Index: extensions/common/switches.cc
diff --git a/extensions/common/switches.cc b/extensions/common/switches.cc
index 23fd19870f09b758754a52b5a704986ad0aef539..773597109038c801169c140294e5e755e0e24336 100644
--- a/extensions/common/switches.cc
+++ b/extensions/common/switches.cc
@@ -99,6 +99,9 @@ const char kShowComponentExtensionOptions[] =
 // Adds the given extension ID to all the permission whitelists.
 const char kWhitelistedExtensionID[] = "whitelisted-extension-id";
 
+// Pass launch source to platform apps.
+const char kTraceAppSource[] = "enable-trace-app-source";
+
 }  // namespace switches
 
 }  // namespace extensions