Rename ActionExitCode to ErrorCode

Nowadays ActionExitCode is used throughout the codebase so use a more
generic name to reflect this.

BUG=chromium:216507
TEST=unit tests pass

Change-Id: I23d1d7e2676443251dbc42ed137fd018aadfa8a3
Reviewed-on: https://gerrit.chromium.org/gerrit/49512
Reviewed-by: Don Garrett <dgarrett@chromium.org>
Commit-Queue: David Zeuthen <zeuthen@chromium.org>
Tested-by: David Zeuthen <zeuthen@chromium.org>
diff --git a/file_writer.h b/file_writer.h
index b9b45e8..57d0498 100644
--- a/file_writer.h
+++ b/file_writer.h
@@ -38,8 +38,8 @@
   // can override if they wish to return more specific error codes.
   virtual bool Write(const void* bytes,
                      size_t count,
-                     ActionExitCode* error) {
-     *error = kActionCodeDownloadWriteError;
+                     ErrorCode* error) {
+     *error = kErrorCodeDownloadWriteError;
      return Write(bytes, count);
   }