Add "Show saved copy" button in dino page when there's offline copy

chrome/common/render_messages.h

 // Copyright (c) 2012 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.
 
 // Multiply-included file, no traditional include guard.
 #include <stdint.h>
 #include <string>
 #include <vector>
 
 #include "base/files/file_path.h"
@@ skipping 305 matching lines @@
 // page with more specific troubleshooting suggestions.
 IPC_MESSAGE_ROUTED1(ChromeViewMsg_NetErrorInfo,
                     int /* DNS probe status */)
 
 // Tells the renderer whether or not there is a local diagnostics service that
 // can be run via ChromeViewHostMsg_RunNetworkDiagnostics messages.
 IPC_MESSAGE_ROUTED1(ChromeViewMsg_SetCanShowNetworkDiagnosticsDialog,
                     bool /* can_show_network_diagnostics_dialog */)
 
 #if defined(OS_ANDROID)
-// Tells the renderer whether or not an offline page exists. This is used to
-// decide if "show saved pages" button will be provided on certain error page.
-IPC_MESSAGE_ROUTED1(ChromeViewMsg_SetHasOfflinePages,
-                    bool /* has_offline_pages */)
-#endif
+// Tells the renderer about the status of the offline pages. This is used to
+// decide if offline related button will be provided on certain error page.
+IPC_MESSAGE_ROUTED1(
+    ChromeViewMsg_SetOfflinePageInfo,
+    std::vector<GURL> /* urls of pages that have offline version */)

[nasko, 2015/11/19 15:11:41]

This should not be done. This leaks unrelated user data into an untrusted
process.

[jianli, 2015/11/19 23:28:08]

We can pass a list of hash values of all URLs. How do you think?

[mmenke, 2015/11/19 23:41:32]

I completely defer to Nasko here, but I wonder...  Are hashes any better here? 
Shouldn't be hard to tell if facebook.com, google.com, etc, are cached, for
instance.

+#endif  // defined(OS_ANDROID)
 
 // Provides the information needed by the renderer process to contact a
 // navigation correction service.  Handled by the NetErrorHelper.
 IPC_MESSAGE_ROUTED5(ChromeViewMsg_SetNavigationCorrectionInfo,
                     GURL /* Navigation correction service base URL */,
                     std::string /* language */,
                     std::string /* origin_country */,
                     std::string /* API key to use */,
                     GURL /* Google Search URL to use */)
 
 IPC_MESSAGE_ROUTED1(ChromeViewHostMsg_RunNetworkDiagnostics,
                     GURL /* failed_url */)
 
 #if defined(OS_ANDROID)
 // Message sent from the renderer to the browser to show the UI for offline
 // pages.
 IPC_MESSAGE_ROUTED0(ChromeViewHostMsg_ShowOfflinePages)
-#endif
+
+// Message sent from the renderer to the browser to load the offline copy of
+// the page that fails to load due to no network connectivity.
+IPC_MESSAGE_ROUTED1(ChromeViewHostMsg_LoadOfflineCopy,
+                    GURL /* url */)
+#endif  // defined(OS_ANDROID)
 
 //-----------------------------------------------------------------------------
 // Misc messages
 // These are messages sent from the renderer to the browser process.
 
 IPC_MESSAGE_CONTROL1(ChromeViewHostMsg_UpdatedCacheStats,
                      blink::WebCache::UsageStats /* stats */)
 
 // Sent by the renderer process to check whether access to FileSystem is
 // granted by content settings.
@@ skipping 220 matching lines @@
 
 // Record a sample string to a Rappor metric.
 IPC_MESSAGE_CONTROL2(ChromeViewHostMsg_RecordRappor,
                      std::string /* metric */,
                      std::string /* sample */)
 
 // Record a domain and registry of a url to a Rappor metric.
 IPC_MESSAGE_CONTROL2(ChromeViewHostMsg_RecordRapporURL,
                      std::string /* metric */,
                      GURL /* sample url */)