Fix webrequest api for webview in webui

<webview> can be directly embedded in a whitelisted webui page, but some
webview apis are broken in a extension-less webui context. This CL fixes:

1. a crash on adding webview.request listener due to null extension pointer.

2. a crash on navigating away from a webview embedder due to dangling zoom observer.

BUG=426016

Review URL: https://codereview.chromium.org/670173002

Cr-Commit-Position: refs/heads/master@{#300897}

1 files changed, 11 insertions, 4 deletions

diff --git a/extensions/browser/extension_function_dispatcher.cc b/extensions/browser/extension_function_dispatcher.cc
index f9bbec5..5edb3ec 100644
--- a/extensions/browser/extension_function_dispatcher.cc
+++ b/extensions/browser/extension_function_dispatcher.cc
@@ -229,8 +229,6 @@ void ExtensionFunctionDispatcher::DispatchOnIOThread(
     const ExtensionHostMsg_Request_Params& params) {
   const Extension* extension =
       extension_info_map->extensions().GetByID(params.extension_id);
-  if (!extension)
-    return;
 
   ExtensionFunction::ResponseCallback callback(
       base::Bind(&IOThreadResponseCallback, ipc_sender, routing_id,
@@ -255,12 +253,21 @@ void ExtensionFunctionDispatcher::DispatchOnIOThread(
   }
   function_io->set_ipc_sender(ipc_sender, routing_id);
   function_io->set_extension_info_map(extension_info_map);
-  function->set_include_incognito(
-      extension_info_map->IsIncognitoEnabled(extension->id()));
+  if (extension) {
+    function->set_include_incognito(
+        extension_info_map->IsIncognitoEnabled(extension->id()));
+  }
 
   if (!CheckPermissions(function.get(), params, callback))
     return;
 
+  if (!extension) {
+    // Skip all of the UMA, quota, event page, activity logging stuff if there
+    // isn't an extension, e.g. if the function call was from WebUI.
+    function->Run()->Execute();
+    return;
+  }
+
   QuotaService* quota = extension_info_map->GetQuotaService();
   std::string violation_error = quota->Assess(extension->id(),
                                               function.get(),