Revert "Revert "Add support for booting with a boot classpath not fully AOTed.""

This reverts commit 14bfeddf2e434954f0ca36687ac0fc5dc6412bd3.

Reason for revert: Removes obsolete DCHECK
Bug: 119800099

Change-Id: Ia984f95300c6b96165f0179bfc2f66b012bf5dbe
diff --git a/dex2oat/dex2oat.cc b/dex2oat/dex2oat.cc
index edefd0a..71f71d1 100644
--- a/dex2oat/dex2oat.cc
+++ b/dex2oat/dex2oat.cc
@@ -808,8 +808,7 @@
     }
 
     if (!IsBootImage() && parser_options->boot_image_filename.empty()) {
-      parser_options->boot_image_filename += android_root_;
-      parser_options->boot_image_filename += "/framework/boot.art";
+      parser_options->boot_image_filename = GetDefaultBootImageLocation(android_root_);
     }
     if (!parser_options->boot_image_filename.empty()) {
       boot_image_filename_ = parser_options->boot_image_filename;