Make InstallObserver methods not pure-virtual

chrome/browser/extensions/install_observer.cc

Index: chrome/browser/extensions/install_observer.cc
diff --git a/chrome/browser/extensions/install_observer.cc b/chrome/browser/extensions/install_observer.cc
index 37c7565cc6b0369e7629de1d3b3778b324d92fe1..7b21419ba6ebcd74f3483cf778b40adf8a442485 100644
--- a/chrome/browser/extensions/install_observer.cc
+++ b/chrome/browser/extensions/install_observer.cc
@@ -19,4 +19,18 @@ InstallObserver::ExtensionInstallParams::ExtensionInstallParams(
           is_platform_app(is_platform_app),
           is_ephemeral(false) {}
 
+void InstallObserver::OnBeginExtensionInstall(
+    const ExtensionInstallParams& params) {}
+void InstallObserver::OnDownloadProgress(const std::string& extension_id,
+                                         int percent_downloaded) {}
+void InstallObserver::OnInstallFailure(const std::string& extension_id) {}
+void InstallObserver::OnExtensionInstalled(const Extension* extension) {}
+void InstallObserver::OnExtensionLoaded(const Extension* extension) {}
+void InstallObserver::OnExtensionUnloaded(const Extension* extension) {}
+void InstallObserver::OnExtensionUninstalled(const Extension* extension) {}
+void InstallObserver::OnAppInstalledToAppList(const std::string& extension_id) {
+}
+void InstallObserver::OnAppsReordered() {}
+void InstallObserver::OnShutdown() {}
+
 }  // namespace extensions