Send Chrome's process id to the app shim.

apps/app_shim/chrome_main_app_mode_mac.mm

Index: apps/app_shim/chrome_main_app_mode_mac.mm
diff --git a/apps/app_shim/chrome_main_app_mode_mac.mm b/apps/app_shim/chrome_main_app_mode_mac.mm
index ddad52a14822ac15e92c6c9d9c53d1c9b0d91bc0..a5e86c5fc032d3d9427e856ca1c1dd87f838f541 100644
--- a/apps/app_shim/chrome_main_app_mode_mac.mm
+++ b/apps/app_shim/chrome_main_app_mode_mac.mm
@@ -21,6 +21,7 @@
 #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"
@@ -432,15 +433,26 @@ int ChromeAppModeStart(const app_mode::ChromeAppModeInfo* info) {
   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;
+  } 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];
+  }
+
+  LOG(INFO) << "pid " << pid;
 
   // 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;