Implement Prohibited App Blocking

Summary:
There are certain 3P apps that are in prohibited categories. For these apps, the server-side currently blocks any incoming signals, but we want to also enforce this blocking on the client-side. In order to do this, we need to use a flag sent from the server-side on the client-side to enable the client to block events from apps that are in prohibited categories (i.e. when this flag is true). This is accomplished by extending the [MobileSdkAppEventsKillSwitchGk](https://www.internalfb.com/code/www/flib/platform/graph/resources/application/mobile_sdk/MobileSdkAppEventsKillSwitchGk.php), which is passed as the ```app_events_killswitch``` flag to the client. More information can be seen [here](https://docs.google.com/document/d/1EYy0vZ-v6q1QDGEDj_N2is6QbX4eDPodI1lYz6W8GEU/), [here](https://docs.google.com/document/d/1MCPIESOxtgTuUJC78DdLeOA8Jv4qiDaWV1NxHzGO34k/), and [here](https://docs.google.com/document/d/1svBR6jklbb6M-lhgh3qj7XyaEchJDn1YXint2ZYU_Fk/).

We already use the ```app_events_killswitch``` flag to block the sending of post-install events. This diff extends the result of the ```app_events_killswitch``` flag to also block install events so that all events are blocked for apps that are in prohibited categories.

Reviewed By: Nathaaaalie

Differential Revision: D51290686

fbshipit-source-id: 573df6453fa705a5290eb9cbef988715ace26034

FBSDKCoreKit/FBSDKCoreKit/AppEvents/FBSDKAppEvents.m

@@ -851,7 +851,7 @@ - (void)publishInstall
     return;
   }
   [self fetchServerConfiguration:^{
-    if ([self.appEventsUtility shouldDropAppEvents]) {
+    if ([self.appEventsUtility shouldDropAppEvents] || [self.gateKeeperManager boolForKey:FBSDKGateKeeperAppEventsKillSwitch defaultValue:NO]) {
       return;
     }
     NSMutableDictionary<NSString *, NSString *> *params = [self.appEventsUtility activityParametersDictionaryForEvent:@"MOBILE_APP_INSTALL"

FBSDKCoreKit/FBSDKCoreKitTests/Internal/AppEvents/AppEventsTests.swift

@@ -570,6 +570,7 @@ final class AppEventsTests: XCTestCase {
   }
 
   func testActivateAppWithInitializedSDK() throws {
+    TestGateKeeperManager.setGateKeeperValue(key: "app_events_killswitch", value: false)
     appEvents.activateApp()
 
     XCTAssertTrue(
@@ -598,6 +599,39 @@ final class AppEventsTests: XCTestCase {
     XCTAssertNotNil(capiReporter.capturedEvent)
   }
 
+  func testActivateAppWithAppEventsKillSwitchEnabled() throws {
+    TestGateKeeperManager.setGateKeeperValue(key: "app_events_killswitch", value: true)
+    appEvents.activateApp()
+
+    XCTAssertTrue(
+      timeSpentRecorder.restoreWasCalled,
+      "Activating App with initialized SDK should restore recording time spent data."
+    )
+    XCTAssertTrue(
+      timeSpentRecorder.capturedCalledFromActivateApp,
+      """
+      Activating App with initialized SDK should indicate its \
+      calling from activateApp when restoring recording time spent data.
+      """
+    )
+
+    // The publish call happens after both configurations are fetched
+    appEventsConfigurationProvider.firstCapturedBlock?()
+    appEventsConfigurationProvider.lastCapturedBlock?()
+    serverConfigurationProvider.capturedCompletionBlock?(nil, nil)
+    serverConfigurationProvider.secondCapturedCompletionBlock?(nil, nil)
+
+    let request = graphRequestFactory.capturedRequests.first
+    XCTAssertNil(
+      request,
+      "No request should be made when the FBSDKGateKeeperAppEventsKillSwitch is enabled"
+    )
+    XCTAssertNil(
+      capiReporter.capturedEvent,
+      "The capiReporter should not be invoked when the FBSDKGateKeeperAppEventsKillSwitch is enabled"
+    )
+  }
+
   func testApplicationBecomingActiveRestoresTimeSpentRecording() {
     appEvents.applicationDidBecomeActive()
     XCTAssertTrue(