Fix memory leak in LoginManager and AppEventsLogger

LoginManager's context and loginLogger both hold a reference to the
activity starting the login. This activity is leaked if the login process
is canceled. It is also leaked if finishLogin() is never called, e.g. when
the device's configuration/orientation is changed. finishLogin() only nulls
out context and loginLogger in case of a successful login.

This commit updates LoginManager and AppEventsLogger, so that it is not
required anymore to hold a reference to the activity starting the login.

facebook/src/com/facebook/appevents/AppEventsLogger.java

@@ -177,7 +177,7 @@ public enum FlushBehavior {
             "_fbSourceApplicationHasBeenSet";
 
     // Instance member variables
-    private final Context context;
+    private final String uiName;
     private final AccessTokenAppIdPair accessTokenAppId;
 
     private static Map<AccessTokenAppIdPair, SessionEventsState> stateMap =
@@ -650,7 +650,7 @@ private enum FlushResult {
      */
     private AppEventsLogger(Context context, String applicationId, AccessToken accessToken) {
         Validate.notNull(context, "context");
-        this.context = context;
+        uiName = Utility.getActivityName(context);
 
         if (accessToken == null) {
             accessToken = AccessToken.getCurrentAccessToken();
@@ -732,12 +732,12 @@ private void logEvent(
             Bundle parameters,
             boolean isImplicitlyLogged) {
         AppEvent event = new AppEvent(
-                this.context,
+                uiName,
                 eventName,
                 valueToSum,
                 parameters,
                 isImplicitlyLogged);
-        logEvent(context, event, accessTokenAppId);
+        logEvent(applicationContext, event, accessTokenAppId);
     }
 
     private static void logEvent(final Context context,
@@ -1290,7 +1290,7 @@ static class AppEvent implements Serializable {
         private String name;
 
         public AppEvent(
-                Context context,
+                String uiName,
                 String eventName,
                 Double valueToSum,
                 Bundle parameters,
@@ -1305,7 +1305,7 @@ public AppEvent(
 
                 jsonObject.put("_eventName", eventName);
                 jsonObject.put("_logTime", System.currentTimeMillis() / 1000);
-                jsonObject.put("_ui", Utility.getActivityName(context));
+                jsonObject.put("_ui", uiName);
 
                 if (valueToSum != null) {
                     jsonObject.put("_valueToSum", valueToSum.doubleValue());

facebook/src/com/facebook/login/LoginManager.java

@@ -63,7 +63,6 @@ public class LoginManager {
     private DefaultAudience defaultAudience = DefaultAudience.FRIENDS;
     private LoginClient.Request pendingLoginRequest;
     private HashMap<String, String> pendingLoggingExtras;
-    private Context context;
     private LoginLogger loginLogger;
 
     LoginManager() {
@@ -355,7 +354,7 @@ private void startLogin(
 
         this.pendingLoginRequest = request;
         this.pendingLoggingExtras = new HashMap<>();
-        this.context = startActivityDelegate.getActivityContext();
+        this.loginLogger = getLoggerForContext(startActivityDelegate.getActivityContext());
 
         logStartLogin();
 
@@ -388,31 +387,36 @@ public boolean onActivityResult(int resultCode, Intent data) {
         }
     }
 
-    private LoginLogger getLogger() {
+    private LoginLogger getLoggerForContext(Context context) {
         if (loginLogger == null ||
                 !loginLogger.getApplicationId().equals(
                         pendingLoginRequest.getApplicationId())) {
-            loginLogger = new LoginLogger(
+            return new LoginLogger(
                     context,
                     pendingLoginRequest.getApplicationId());
         }
         return loginLogger;
     }
 
     private void logStartLogin() {
-        getLogger().logStartLogin(pendingLoginRequest);
+        if (loginLogger != null) {
+            loginLogger.logStartLogin(pendingLoginRequest);
+        }
     }
 
     private void logCompleteLogin(LoginClient.Result.Code result, Map<String, String> resultExtras,
                                   Exception exception) {
+        if (loginLogger == null) {
+            return;
+        }
         if (pendingLoginRequest == null) {
             // We don't expect this to happen, but if it does, log an event for diagnostic purposes.
-            getLogger().logUnexpectedError(
-                LoginLogger.EVENT_NAME_LOGIN_COMPLETE,
-                "Unexpected call to logCompleteLogin with null pendingAuthorizationRequest."
+            loginLogger.logUnexpectedError(
+                    LoginLogger.EVENT_NAME_LOGIN_COMPLETE,
+                    "Unexpected call to logCompleteLogin with null pendingAuthorizationRequest."
             );
         } else {
-            getLogger().logCompleteLogin(
+            loginLogger.logCompleteLogin(
                     pendingLoginRequest.getAuthId(),
                     pendingLoggingExtras,
                     result,
@@ -501,18 +505,12 @@ private void finishLogin(
                     || (loginResult != null
                            && loginResult.getRecentlyGrantedPermissions().size() == 0)) {
                 callback.onCancel();
-                return;
-            }
-            if (exception != null) {
+            } else if (exception != null) {
                 callback.onError(exception);
             } else if (newToken != null) {
                 callback.onSuccess(loginResult);
             }
         }
-
-        // Cleanup saved context to avoid leaking
-        this.context = null;
-        this.loginLogger = null;
     }
 
     private static class ActivityStartActivityDelegate implements StartActivityDelegate {