Add chrome.webstore API methods to allow sites to see progress of installation

chrome/browser/extensions/install_observer.h

Index: chrome/browser/extensions/install_observer.h
diff --git a/chrome/browser/extensions/install_observer.h b/chrome/browser/extensions/install_observer.h
index 6c64cca7e815e66eef55ca3c09ae1f6b92f37e1d..6622dddfd6e9748b9e2296d429a3769e559b7b0b 100644
--- a/chrome/browser/extensions/install_observer.h
+++ b/chrome/browser/extensions/install_observer.h
@@ -33,34 +33,43 @@ class InstallObserver {
 
   // Called at the beginning of the complete installation process, i.e., this
   // is called before the extension download begins.
-  virtual void OnBeginExtensionInstall(const ExtensionInstallParams& params);
+  virtual void OnBeginExtensionInstall(const ExtensionInstallParams& params) {}
+
+  // Called when the Extension begins the download process. This typically
+  // happens right after OnBeginExtensionInstall(), unless the extension has
+  // already been downloaded.
+  virtual void OnBeginExtensionDownload(const std::string& extension_id) {}
 
   // Called whenever the extension download is updated.
   // Note: Some extensions have multiple modules, so the percent included here
   // is a simple calculation of:
   // (finished_files * 100 + current_file_progress) / (total files * 100).
   virtual void OnDownloadProgress(const std::string& extension_id,
-                                  int percent_downloaded);
+                                  int percent_downloaded) {}
+
+  // Called when the necessary downloads have completed, and the crx
+  // installation is due to start.
+  virtual void OnBeginCrxInstall(const std::string& extension_id) {}
 
   // Called if the extension fails to install.
-  virtual void OnInstallFailure(const std::string& extension_id);
+  virtual void OnInstallFailure(const std::string& extension_id) {}
 
   // Called if the installation succeeds.
-  virtual void OnExtensionInstalled(const Extension* extension);
+  virtual void OnExtensionInstalled(const Extension* extension) {}
 
   // Called when an extension is [Loaded, Unloaded, Uninstalled] or an app is
   // installed to the app list. These are simply forwarded from the
   // chrome::NOTIFICATIONs.
-  virtual void OnExtensionLoaded(const Extension* extension);
-  virtual void OnExtensionUnloaded(const Extension* extension);
-  virtual void OnExtensionUninstalled(const Extension* extension);
-  virtual void OnAppInstalledToAppList(const std::string& extension_id);
+  virtual void OnExtensionLoaded(const Extension* extension) {}
+  virtual void OnExtensionUnloaded(const Extension* extension) {}
+  virtual void OnExtensionUninstalled(const Extension* extension) {}
+  virtual void OnAppInstalledToAppList(const std::string& extension_id) {}
 
   // Called when the app list is reordered.
-  virtual void OnAppsReordered();
+  virtual void OnAppsReordered() {}
 
   // Notifies observers that the observed object is going away.
-  virtual void OnShutdown();
+  virtual void OnShutdown() {}
 
  protected:
   virtual ~InstallObserver() {}