Perform all iOS logging through ASL

lib/ui/dart_runtime_hooks.cc

@@ -28,10 +28,7 @@
 #endif
 
 #if __APPLE__
-extern "C" {
-// Cannot import the syslog.h header directly because of macro collision
-extern void syslog(int, const char*, ...);
-}
+#include <asl.h>
 #endif
 
 using tonic::LogIfError;
@@ -157,7 +154,7 @@ void Logger_PrintString(Dart_NativeArguments args) {
     __android_log_print(ANDROID_LOG_INFO, tag, "%.*s", (int)length,
                         chars);
 #elif __APPLE__
-    syslog(1 /* LOG_ALERT */, "%.*s", (int)length, chars);
+    asl_log_message(ASL_LEVEL_NOTICE, "%.*s", (int)length, chars);
 #endif
   }
   if (dart::bin::ShouldCaptureStdout()) {

shell/common/switches.h

@@ -62,6 +62,11 @@ DEF_SWITCH(NonInteractive,
            "non-interactive",
            "Make the shell non-interactive. By default, the shell attempts "
            "to setup a window and create an OpenGL context.")
+DEF_SWITCH(NoRedirectToSyslog,
+           "no-redirect-to-syslog",
+           "On iOS: Don't redirect stdout and stderr to syslog by default. "
+           "This is used by the tools to read device logs. However, this can "
+           "cause logs to not show up when launched from Xcode.")
 DEF_SWITCH(Packages, "packages", "Specify the path to the packages.")
 DEF_SWITCH(StartPaused,
            "start-paused",

shell/platform/darwin/common/platform_mac.mm

@@ -36,6 +36,20 @@ static void InitializeLogging() {
                        false);  // Tick count
 }
 
+static void RedirectIOConnectionsToSyslog() {
+#if TARGET_OS_IPHONE
+  if (base::CommandLine::ForCurrentProcess()->HasSwitch(
+          FlagForSwitch(Switch::NoRedirectToSyslog))) {
+    return;
+  }
+
+  asl_log_descriptor(NULL, NULL, ASL_LEVEL_NOTICE, STDOUT_FILENO,
+                     ASL_LOG_DESCRIPTOR_WRITE);
+  asl_log_descriptor(NULL, NULL, ASL_LEVEL_WARNING, STDERR_FILENO,
+                     ASL_LOG_DESCRIPTOR_WRITE);
+#endif
+}
+
 static void InitializeCommandLine() {
   base::mac::ScopedNSAutoreleasePool pool;
   base::CommandLine::StringVector vector;
@@ -63,6 +77,8 @@ static void InitializeCommandLine() {
 
     InitializeCommandLine();
 
+    RedirectIOConnectionsToSyslog();
+
     InitializeLogging();
 
     base::CommandLine& command_line = *base::CommandLine::ForCurrentProcess();