Add ApiActivityMonitor to decouple ActivityLog from low-level extensions code

apps/shell/browser/shell_extensions_browser_client.cc

Index: apps/shell/browser/shell_extensions_browser_client.cc
diff --git a/apps/shell/browser/shell_extensions_browser_client.cc b/apps/shell/browser/shell_extensions_browser_client.cc
index 0ed1f1b64386d816c762dad50a8e4b6b12149672..079e5a05464968cfac8ba2ab697ecb58f1b3a76c 100644
--- a/apps/shell/browser/shell_extensions_browser_client.cc
+++ b/apps/shell/browser/shell_extensions_browser_client.cc
@@ -122,6 +122,12 @@ ShellExtensionsBrowserClient::GetJavaScriptDialogManager() {
   return NULL;
 }
 
+ApiActivityMonitor* ShellExtensionsBrowserClient::GetApiActivityMonitor(
+    BrowserContext* context) {
+  // app_shell doesn't monitor API function calls or events.
+  return NULL;
+}
+
 std::vector<BrowserContextKeyedServiceFactory*>
 ShellExtensionsBrowserClient::GetExtensionSystemDependencies() {
   return ShellExtensionSystem::GetDependencies();