[CRD iOS] Disable video channel when app goes to background

Make HostViewController call EnableVideoChannel(false) when the app is
inactive. This can save some battery for the device.

Bug: 824554
Change-Id: Ic468344509bcb9458a592cf4eea8e5b28a939f90
Reviewed-on: https://chromium-review.googlesource.com/974506Reviewed-by: Jamie Walch <jamiewalch@chromium.org>
Commit-Queue: Yuwei Huang <yuweih@chromium.org>
Cr-Commit-Position: refs/heads/master@{#544957}

remoting/client/chromoting_session.h

@@ -130,7 +130,7 @@ class ChromotingSession : public ClientInputInjector {
 
   void SendClientResolution(int dips_width, int dips_height, int scale);
 
-  // Enables or disables the video channel. May be called from any thread.
+  // Enables or disables the video channel.
   void EnableVideoChannel(bool enable);
 
   void SendClientMessage(const std::string& type, const std::string& data);

remoting/ios/app/host_view_controller.mm

@@ -640,6 +640,7 @@ static NSString* const kFeedbackContext = @"InSessionFeedbackContext";
     LOG(DFATAL) << "Blur view does not exist.";
     return;
   }
+  [_client setVideoChannelEnabled:YES];
   [_blurView removeFromSuperview];
   _blurView = nil;
 }
@@ -660,6 +661,7 @@ static NSString* const kFeedbackContext = @"InSessionFeedbackContext";
     [_blurView.topAnchor constraintEqualToAnchor:_hostView.topAnchor],
     [_blurView.bottomAnchor constraintEqualToAnchor:_hostView.bottomAnchor],
   ]];
+  [_client setVideoChannelEnabled:NO];
 }
 
 @end

remoting/ios/session/remoting_client.h

@@ -75,6 +75,8 @@ extern NSString* const kHostSessionPin;
 
 - (void)setHostResolution:(CGSize)dipsResolution scale:(int)scale;
 
+- (void)setVideoChannelEnabled:(BOOL)enabled;
+
 // Creates a feedback data and returns it to the callback.
 - (void)createFeedbackDataWithCallback:
     (void (^)(const remoting::FeedbackData&))callback;

remoting/ios/session/remoting_client.mm

@@ -359,6 +359,10 @@ static void ResolveFeedbackDataCallback(
                                  scale);
 }
 
+- (void)setVideoChannelEnabled:(BOOL)enabled {
+  _session->EnableVideoChannel(enabled);
+}
+
 - (void)createFeedbackDataWithCallback:
     (void (^)(const remoting::FeedbackData&))callback {
   if (!_session) {