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

chrome/common/render_messages.h

Index: chrome/common/render_messages.h
diff --git a/chrome/common/render_messages.h b/chrome/common/render_messages.h
index e096a931ac55f5f02da1eea0fb22de14d0c6336d..c4ac7271cd7e310bf12832a24dba44100a986f62 100644
--- a/chrome/common/render_messages.h
+++ b/chrome/common/render_messages.h
@@ -323,11 +323,12 @@ 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.
@@ -345,7 +346,12 @@ IPC_MESSAGE_ROUTED1(ChromeViewHostMsg_RunNetworkDiagnostics,
 // 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