content_shell/app_shell: validate --data-path and fall back to default directory

content/shell/browser/shell_browser_context.cc

Index: content/shell/browser/shell_browser_context.cc
diff --git a/content/shell/browser/shell_browser_context.cc b/content/shell/browser/shell_browser_context.cc
index 65f4801b923a385b74fa8ff53bab720a5810f48d..55dd1017e05f863d2cb39592b1eecdab7ddd4f9d 100644
--- a/content/shell/browser/shell_browser_context.cc
+++ b/content/shell/browser/shell_browser_context.cc
@@ -75,9 +75,19 @@ void ShellBrowserContext::InitWhileIOAllowed() {
     ignore_certificate_errors_ = true;
   if (cmd_line->HasSwitch(switches::kContentShellDataPath)) {
     path_ = cmd_line->GetSwitchValuePath(switches::kContentShellDataPath);
-    BrowserContext::Initialize(this, path_);
-    return;
+    if (base::DirectoryExists(path_) || base::CreateDirectory(path_))  {
+      // We need to have an absolute path.

[Peter Beverloo, 2016/09/29 16:22:53]

nit: might be good to document that the PathService normally takes care of this,
and features therefore might assume this to be the case.

[michaelpg, 2016/09/30 03:38:56]

Done.

+      if (!path_.IsAbsolute())
+        path_ = base::MakeAbsoluteFilePath(path_);
+      if (!path_.empty()) {
+        BrowserContext::Initialize(this, path_);
+        return;
+      }
+    } else {
+      LOG(WARNING) << "Unable to create data-path directory: " << path_.value();
+    }
   }
+
 #if defined(OS_WIN)
   CHECK(PathService::Get(base::DIR_LOCAL_APP_DATA, &path_));
   path_ = path_.Append(std::wstring(L"content_shell"));