Enforce cache_path requirements for NetworkService (see issue #2622).

This change adds a new CefSettings.root_cache_path value that must be either
equal to or a parent directory of all CefSettings.cache_path and
CefRequestContextSettings.cache_path values. The sandbox may block read/write
access from the NetworkService to directories that do not meet this requirement.

To test: Run cefclient with a combination of the following flags:

--cache-path=c:\temp\cache
  Cache data should be persisted to the specified directory.

--request-context-per-browser
  A separate numbered cache directory should be created underneath the
  cache-path directory for each new browser instance.

--enable-network-service --disable-extensions
  Same tests, but with NetworkService enabled.

Known issues:
- When NetworkService is enabled a C:\temp\cache\cache\Cache directory is
  created (should be C:\temp\cache\Cache).

tests/cefclient/browser/dialog_test.cc

@@ -9,6 +9,7 @@
 #include "include/cef_browser.h"
 #include "include/wrapper/cef_helpers.h"
 #include "tests/cefclient/browser/test_runner.h"
+#include "tests/shared/browser/file_util.h"
 
 namespace client {
 namespace dialog_test {
@@ -21,12 +22,6 @@ const char kFileOpenMultipleMessageName[] = "DialogTest.FileOpenMultiple";
 const char kFileOpenFolderMessageName[] = "DialogTest.FileOpenFolder";
 const char kFileSaveMessageName[] = "DialogTest.FileSave";
 
-#if defined(OS_WIN)
-#define PATH_SEP '\\'
-#else
-#define PATH_SEP '/'
-#endif
-
 // Store persistent dialog state information.
 class DialogState : public base::RefCountedThreadSafe<DialogState> {
  public:
@@ -62,10 +57,10 @@ class DialogCallback : public CefRunFileDialogCallback {
       dialog_state_->last_file_ = file_paths[0];
       if (dialog_state_->mode_ == FILE_DIALOG_OPEN_FOLDER) {
         std::string last_file = dialog_state_->last_file_;
-        if (last_file[last_file.length() - 1] != PATH_SEP) {
+        if (last_file[last_file.length() - 1] != file_util::kPathSep) {
           // Add a trailing slash so we know it's a directory. Otherwise, file
           // dialogs will think the last path component is a file name.
-          last_file += PATH_SEP;
+          last_file += file_util::kPathSep;
           dialog_state_->last_file_ = last_file;
         }
       }