Add status code "Bad Request" (400).

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=141460113

Author: FanghuiQ

google-http-client/src/main/java/com/google/api/client/http/HttpStatusCodes.java

@@ -51,6 +51,9 @@ public class HttpStatusCodes {
   /** Status code for a resource that has temporarily moved to a new URI. */
   public static final int STATUS_CODE_TEMPORARY_REDIRECT = 307;
 
+  /** Status code for a request that could not be understood by the server. */
+  public static final int STATUS_CODE_BAD_REQUEST = 400;
+
   /** Status code for a request that requires user authentication. */
   public static final int STATUS_CODE_UNAUTHORIZED = 401;