Make list_files.py and list_dart_files.py return absolute paths for GN

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index a027a2e6150b25e0778b0dc9e779488b0401dfbd..7d1f7fd87645575525b854fec12285f08bcca098 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -70,12 +70,13 @@ action("create_sdk") {
   ]
 
   sdk_lib_files = exec_script("tools/list_dart_files.py",
-                              [ rebase_path("sdk/lib") ],
+                              [ "absolute", rebase_path("sdk/lib") ],
                               "list lines")
 
   preamble_files =
       exec_script("tools/list_files.py",
                   [
+                    "absolute",
                     "",
                     rebase_path("sdk/lib/_internal/js_runtime/lib/preambles"),
                   ],
@@ -83,14 +84,13 @@ action("create_sdk") {
 
   sdk_bin_files = exec_script("tools/list_files.py",
                               [
+                                "absolute",
                                 "",
                                 rebase_path("sdk/bin"),
                               ],
                               "list lines")
 
-  inputs = rebase_path(sdk_lib_files, "", "sdk/lib") +
-           rebase_path(preamble_files, "", "sdk/lib") +
-           rebase_path(sdk_bin_files, "", "sdk/bin") +
+  inputs = sdk_lib_files + preamble_files + sdk_bin_files +
            [
              "sdk/lib/dart_client.platform",
              "sdk/lib/dart_server.platform",