Cache failover to LOAD_PREFERRING_CACHE if network response suggests offline.

net/base/load_flags_list.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This is the list of load flags and their values. For the enum values,
 // include the file "net/base/load_flags.h".
 //
 // Here we define the values using a macro LOAD_FLAG, so it can be
 // expanded differently in some places (for example, to automatically
 // map a load flag value to its symbolic name).
 
 LOAD_FLAG(NORMAL, 0)
 
 // This is "normal reload", meaning an if-none-match/if-modified-since query
 LOAD_FLAG(VALIDATE_CACHE, 1 << 0)
 
 // This is "shift-reload", meaning a "pragma: no-cache" end-to-end fetch
 LOAD_FLAG(BYPASS_CACHE, 1 << 1)
 
 // This is a back/forward style navigation where the cached content should
 // be preferred over any protocol specific cache validation.
 LOAD_FLAG(PREFERRING_CACHE, 1 << 2)
 
 // This is a navigation that will fail if it cannot serve the requested
 // resource from the cache (or some equivalent local store).
 LOAD_FLAG(ONLY_FROM_CACHE, 1 << 3)
 
+// Indicate that if the request fails at the network level in a way that
+// indicates the source is unreachable, the request should fail over
+// to as if LOAD_PREFERRING_CACHE had been set.
+LOAD_FLAG(FROM_CACHE_IF_OFFLINE, 1 << 4)
+
 // This is a navigation that will not use the cache at all.  It does not
 // impact the HTTP request headers.
-LOAD_FLAG(DISABLE_CACHE, 1 << 4)
+LOAD_FLAG(DISABLE_CACHE, 1 << 5)
 
 // This is a navigation that will not be intercepted by any registered
 // URLRequest::Interceptors.
-LOAD_FLAG(DISABLE_INTERCEPT, 1 << 5)
+LOAD_FLAG(DISABLE_INTERCEPT, 1 << 6)
 
 // If present, upload progress messages should be provided to initiator.
-LOAD_FLAG(ENABLE_UPLOAD_PROGRESS, 1 << 6)
+LOAD_FLAG(ENABLE_UPLOAD_PROGRESS, 1 << 7)
 
 // If present, collect load timing for the request.
-LOAD_FLAG(ENABLE_LOAD_TIMING, 1 << 7)
+LOAD_FLAG(ENABLE_LOAD_TIMING, 1 << 8)
 
 // If present, ignores certificate mismatches with the domain name.
 // (The default behavior is to trigger an OnSSLCertificateError callback.)
-LOAD_FLAG(IGNORE_CERT_COMMON_NAME_INVALID, 1 << 8)
+LOAD_FLAG(IGNORE_CERT_COMMON_NAME_INVALID, 1 << 9)
 
 // If present, ignores certificate expiration dates
 // (The default behavior is to trigger an OnSSLCertificateError callback).
-LOAD_FLAG(IGNORE_CERT_DATE_INVALID, 1 << 9)
+LOAD_FLAG(IGNORE_CERT_DATE_INVALID, 1 << 10)
 
 // If present, trusts all certificate authorities
 // (The default behavior is to trigger an OnSSLCertificateError callback).
-LOAD_FLAG(IGNORE_CERT_AUTHORITY_INVALID, 1 << 10)
+LOAD_FLAG(IGNORE_CERT_AUTHORITY_INVALID, 1 << 11)
 
 // If present, causes certificate revocation checks to be skipped on secure
 // connections.
-LOAD_FLAG(DISABLE_CERT_REVOCATION_CHECKING, 1 << 11)
+LOAD_FLAG(DISABLE_CERT_REVOCATION_CHECKING, 1 << 12)
 
 // If present, ignores wrong key usage of the certificate
 // (The default behavior is to trigger an OnSSLCertificateError callback).
-LOAD_FLAG(IGNORE_CERT_WRONG_USAGE, 1 << 12)
+LOAD_FLAG(IGNORE_CERT_WRONG_USAGE, 1 << 13)
 
 // This load will not make any changes to cookies, including storing new
 // cookies or updating existing ones.
-LOAD_FLAG(DO_NOT_SAVE_COOKIES, 1 << 13)
+LOAD_FLAG(DO_NOT_SAVE_COOKIES, 1 << 14)
 
 // Do not resolve proxies. This override is used when downloading PAC files
 // to avoid having a circular dependency.
-LOAD_FLAG(BYPASS_PROXY, 1 << 14)
+LOAD_FLAG(BYPASS_PROXY, 1 << 15)
 
 // Indicate this request is for a download, as opposed to viewing.
-LOAD_FLAG(IS_DOWNLOAD, 1 << 15)
+LOAD_FLAG(IS_DOWNLOAD, 1 << 16)
 
 // Requires EV certificate verification.
-LOAD_FLAG(VERIFY_EV_CERT, 1 << 16)
+LOAD_FLAG(VERIFY_EV_CERT, 1 << 17)
 
 // This load will not send any cookies.
-LOAD_FLAG(DO_NOT_SEND_COOKIES, 1 << 17)
+LOAD_FLAG(DO_NOT_SEND_COOKIES, 1 << 18)
 
 // This load will not send authentication data (user name/password)
 // to the server (as opposed to the proxy).
-LOAD_FLAG(DO_NOT_SEND_AUTH_DATA, 1 << 18)
+LOAD_FLAG(DO_NOT_SEND_AUTH_DATA, 1 << 19)
 
 // This should only be used for testing (set by HttpNetworkTransaction).
-LOAD_FLAG(IGNORE_ALL_CERT_ERRORS, 1 << 19)
+LOAD_FLAG(IGNORE_ALL_CERT_ERRORS, 1 << 20)
 
 // Indicate that this is a top level frame, so that we don't assume it is a
 // subresource and speculatively pre-connect or pre-resolve when a referring
 // page is loaded.
-LOAD_FLAG(MAIN_FRAME, 1 << 20)
+LOAD_FLAG(MAIN_FRAME, 1 << 21)
 
 // Indicate that this is a sub frame, and hence it might have subresources that
 // should be speculatively resolved, or even speculatively preconnected.
-LOAD_FLAG(SUB_FRAME, 1 << 21)
+LOAD_FLAG(SUB_FRAME, 1 << 22)
 
 // If present, intercept actual request/response headers from network stack
 // and report them to renderer. This includes cookies, so the flag is only
 // respected if renderer has CanReadRawCookies capability in the security
 // policy.
-LOAD_FLAG(REPORT_RAW_HEADERS, 1 << 22)
+LOAD_FLAG(REPORT_RAW_HEADERS, 1 << 23)
 
 // Indicates that this load was motivated by the rel=prefetch feature,
 // and is (in theory) not intended for the current frame.
-LOAD_FLAG(PREFETCH, 1 << 23)
+LOAD_FLAG(PREFETCH, 1 << 24)
 
 // Indicates that this is a load that ignores limits and should complete
 // immediately.
-LOAD_FLAG(IGNORE_LIMITS, 1 << 24)
+LOAD_FLAG(IGNORE_LIMITS, 1 << 25)
 
 // Suppress login prompts for this request. Cached credentials or
 // default credentials may still be used for authentication.
-LOAD_FLAG(DO_NOT_PROMPT_FOR_LOGIN, 1 << 25)
+LOAD_FLAG(DO_NOT_PROMPT_FOR_LOGIN, 1 << 26)
 
 // Indicates that the operation is somewhat likely to be due to an
 // explicit user action. This can be used as a hint to treat the
 // request with higher priority.
-LOAD_FLAG(MAYBE_USER_GESTURE, 1 << 26)
+LOAD_FLAG(MAYBE_USER_GESTURE, 1 << 27)