Send Chrome's process id to the app shim.

apps/app_shim/chrome_main_app_mode_mac.mm

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // On Mac, one can't make shortcuts with command-line arguments. Instead, we
 // produce small app bundles which locate the Chromium framework and load it,
 // passing the appropriate data. This is the entry point into the framework for
 // those app bundles.
 
 #import <Cocoa/Cocoa.h>
 
 #include "apps/app_shim/app_shim_messages.h"
 #include "base/at_exit.h"
 #include "base/command_line.h"
 #include "base/logging.h"
 #include "base/mac/bundle_locations.h"
 #include "base/mac/launch_services_util.h"
 #include "base/mac/mac_logging.h"
 #include "base/mac/mac_util.h"
 #include "base/mac/scoped_nsautorelease_pool.h"
 #include "base/mac/scoped_nsobject.h"
 #include "base/message_loop/message_loop.h"
 #include "base/path_service.h"
+#include "base/strings/string_number_conversions.h"
 #include "base/strings/sys_string_conversions.h"
 #include "base/threading/thread.h"
 #include "chrome/common/chrome_constants.h"
 #include "chrome/common/chrome_paths.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/mac/app_mode_common.h"
 #include "grit/generated_resources.h"
 #include "ipc/ipc_channel_proxy.h"
 #include "ipc/ipc_listener.h"
 #include "ipc/ipc_message.h"
@@ skipping 391 matching lines @@
   ResourceBundle::InitSharedInstanceLocaleOnly(locale, NULL);
 
   // Launch the IO thread.
   base::Thread::Options io_thread_options;
   io_thread_options.message_loop_type = base::MessageLoop::TYPE_IO;
   base::Thread *io_thread = new base::Thread("CrAppShimIO");
   io_thread->StartWithOptions(io_thread_options);
   g_io_thread = io_thread;
 
   // Find already running instances of Chrome.
-  NSString* chrome_bundle_id = [base::mac::OuterBundle() bundleIdentifier];
-  NSArray* existing_chrome = [NSRunningApplication
-      runningApplicationsWithBundleIdentifier:chrome_bundle_id];
+  pid_t pid = -1;
+  std::string chrome_process_id = CommandLine::ForCurrentProcess()->
+      GetSwitchValueASCII(app_mode::kChromeProcessId);
+  if (!chrome_process_id.empty()) {
+    if (!base::StringToInt(chrome_process_id, &pid))
+      pid = -1;

[tapted, 2013/08/22 06:17:12]

This implies it will try to start a new Chrome.. Maybe LOG(FATAL) << "Invalid
PID"  (or `return EXIT_FAILURE;`)?  i.e., if this argument is present it means
it came from a running chrome, and so we should never start a new one.

[jackhou1, 2013/08/22 06:52:53]

Done.

+  } else {
+    NSString* chrome_bundle_id = [base::mac::OuterBundle() bundleIdentifier];
+    NSArray* existing_chrome = [NSRunningApplication
+        runningApplicationsWithBundleIdentifier:chrome_bundle_id];
+    if ([existing_chrome count] > 0)
+      pid = [[existing_chrome objectAtIndex:0] processIdentifier];
+  }
 
   // Launch Chrome if it isn't already running.
   ProcessSerialNumber psn;
-  if ([existing_chrome count] > 0) {
-    OSStatus status = GetProcessForPID(
-        [[existing_chrome objectAtIndex:0] processIdentifier], &psn);
+  if (pid > -1) {
+    OSStatus status = GetProcessForPID(pid, &psn);
     if (status)
       return 1;
 
   } else {
     CommandLine command_line(CommandLine::NO_PROGRAM);
     command_line.AppendSwitch(switches::kSilentLaunch);
     command_line.AppendSwitchPath(switches::kProfileDirectory,
                                   info->profile_dir);
     bool success =
         base::mac::OpenApplicationWithPath(base::mac::OuterBundlePath(),
                                            command_line,
                                            kLSLaunchDefaults,
                                            &psn);
     if (!success)
       return 1;
   }
 
   // This code abuses the fact that Apple Events sent before the process is
   // fully initialized don't receive a reply until its run loop starts. Once
   // the reply is received, Chrome will have opened its IPC port, guaranteed.
   [ReplyEventHandler pingProcess:psn andCall:base::Bind(&OnPingChromeReply)];
 
   base::MessageLoopForUI main_message_loop;
   main_message_loop.set_thread_name("MainThread");
   base::PlatformThread::SetName("CrAppShimMain");
   main_message_loop.Run();
   return 0;
 }