Re-commit r22981 after backout at r22992

chrome/common/child_process_host.cc

Index: chrome/common/child_process_host.cc
===================================================================
--- chrome/common/child_process_host.cc	(revision 22996)
+++ chrome/common/child_process_host.cc	(working copy)
@@ -4,13 +4,17 @@
 
 #include "chrome/common/child_process_host.h"
 
+#include "base/command_line.h"
 #include "base/compiler_specific.h"
+#include "base/file_path.h"
 #include "base/logging.h"
 #include "base/message_loop.h"
+#include "base/path_service.h"
 #include "base/process_util.h"
 #include "base/singleton.h"
 #include "base/waitable_event.h"
 #include "chrome/browser/chrome_thread.h"
+#include "chrome/common/chrome_switches.h"
 #include "chrome/common/notification_service.h"
 #include "chrome/common/notification_type.h"
 #include "chrome/common/plugin_messages.h"
@@ -65,6 +69,67 @@
     ProcessWatcher::EnsureProcessTerminated(handle());
 }
 
+// static
+std::wstring ChildProcessHost::GetChildPath() {
+  std::wstring child_path = CommandLine::ForCurrentProcess()->GetSwitchValue(
+      switches::kBrowserSubprocessPath);
+  if (!child_path.empty())
+    return child_path;
+
+#if !defined(OS_MACOSX)
+  // On most platforms, the child executable is the same as the current
+  // executable.
+  PathService::Get(base::FILE_EXE, &child_path);
+  return child_path;
+#else
+  // On the Mac, the child executable lives at a predefined location within
+  // the current app bundle.
+
+  FilePath path;
+  if (!PathService::Get(base::FILE_EXE, &path))
+    return child_path;
+
+  // Figure out the current executable name.  In a browser, this will be
+  // "Chromium" or "Google Chrome".  The child name will be the browser
+  // executable name with " Helper" appended.  The child app bundle name will
+  // be that name with ".app" appended.
+  FilePath::StringType child_exe_name = path.BaseName().value();
+  const FilePath::StringType child_suffix = FILE_PATH_LITERAL(" Helper");
+
+  if (child_exe_name.size() > child_suffix.size()) {
+    size_t test_suffix_pos = child_exe_name.size() - child_suffix.size();
+    const FilePath::CharType* test_suffix =
+        child_exe_name.c_str() + test_suffix_pos;
+    if (strcmp(test_suffix, child_suffix.c_str()) == 0) {
+      // FILE_EXE already ends with the child suffix and therefore already
+      // refers to the child process path.  Just return it.
+      return path.ToWStringHack();
+    }
+  }
+
+  child_exe_name.append(child_suffix);
+  FilePath::StringType child_app_name = child_exe_name;
+  child_app_name.append(FILE_PATH_LITERAL(".app"));
+  // The renderer app bundle lives in the browser app bundle's Resources
+  // directory.  Take off the executable name.
+  path = path.DirName();
+
+  // Take off the MacOS component, after verifying that's what's there.
+  FilePath::StringType macos = path.BaseName().value();
+  DCHECK_EQ(macos, FILE_PATH_LITERAL("MacOS"));
+  path = path.DirName();
+
+  // Append the components to get to the sub-app bundle's executable.
+  path = path.Append(FILE_PATH_LITERAL("Resources"));
+  path = path.Append(child_app_name);
+  path = path.Append(FILE_PATH_LITERAL("Contents"));
+  path = path.Append(FILE_PATH_LITERAL("MacOS"));
+  path = path.Append(child_exe_name);
+
+  return path.ToWStringHack();
+#endif  // OS_MACOSX
+}
+
 bool ChildProcessHost::CreateChannel() {
   channel_id_ = GenerateRandomChannelID(this);
   channel_.reset(new IPC::Channel(