Forcefully disabling renderer accesibility (#660)

* Forcefully disabling renderer accesibility as this is leading to performance issues with Windows update  KB4343909

* Conditionally adding disable-renderer-accessibility flag based on wheter the user has passed on --force-renderer-accessibility or --enable-renderer-accessibility

* Code cleanup and fixed documentation.

* Restricting the accessibility option only to Windows.

appshell/cefclient.cpp

@@ -20,6 +20,10 @@
 
 CefRefPtr<ClientHandler> g_handler;
 
+#ifdef OS_WIN
+bool g_force_enable_acc = false;
+#endif
+
 CefRefPtr<CefBrowser> AppGetBrowser() {
   if (!g_handler.get())
     return NULL;
@@ -32,6 +36,20 @@ CefWindowHandle AppGetMainHwnd() {
   return g_handler->GetMainHwnd();
 }
 
+// CefCommandLine::HasSwitch is unable to report the presense of switches,
+// in the command line properly. This is a generic function that could be
+// used to check for any particular switch, passed as a command line argument.
+bool HasSwitch(CefRefPtr<CefCommandLine> command_line , CefString& switch_name)
+{
+  if (command_line) {
+    ExtensionString cmdLine = command_line->GetCommandLineString();
+    size_t idx = cmdLine.find(switch_name);
+    return idx > 0 && idx < cmdLine.length();
+  } else {
+    return false;
+  }
+}
+
 // Returns the application settings based on command line arguments.
 void AppGetSettings(CefSettings& settings, CefRefPtr<CefCommandLine> command_line) {
   DCHECK(command_line.get());
@@ -91,4 +109,16 @@ void AppGetSettings(CefSettings& settings, CefRefPtr<CefCommandLine> command_lin
     // Set product version, which gets added to the User Agent string
     CefString(&settings.product_version) = versionStr;
   }
+
+#ifdef OS_WIN
+  // We disable renderer accessibility by default as it is known to cause performance
+  // issues. But if any one wants to enable it back, then we need to honor the flag.
+
+  CefString force_acc_switch_name("--force-renderer-accessibility");
+  CefString enable_acc_switch_name("--enable-renderer-accessibility");
+
+  if (HasSwitch(command_line, force_acc_switch_name) || HasSwitch(command_line, enable_acc_switch_name))
+    g_force_enable_acc = true;
+#endif
+
 }

appshell/client_app.cpp

@@ -16,6 +16,10 @@
 #include "appshell/appshell_extension_handler.h"
 #include "appshell/appshell_helpers.h"
 
+#ifdef OS_WIN
+extern bool g_force_enable_acc;
+#endif
+
 ClientApp::ClientApp() {
   CreateRenderDelegates(render_delegates_);
 }
@@ -42,6 +46,27 @@ void ClientApp::OnContextCreated(CefRefPtr<CefBrowser> browser,
     (*it)->OnContextCreated(this, browser, frame, context);
 }
 
+void ClientApp::OnBeforeCommandLineProcessing(
+	const CefString& process_type,
+	CefRefPtr<CefCommandLine> command_line)
+{
+ #ifdef OS_WIN
+  // Check if the user wants to enable renderer accessibility
+  // and if not, then disable renderer accessibility.
+  if (!g_force_enable_acc)
+    command_line->AppendSwitch("disable-renderer-accessibility");
+ #endif
+}
+
+void ClientApp::OnBeforeChildProcessLaunch(
+	CefRefPtr<CefCommandLine> command_line)
+{
+#ifdef OS_WIN
+  if (!g_force_enable_acc)
+    command_line->AppendSwitch("disable-renderer-accessibility");
+#endif
+}
+
 void ClientApp::OnContextReleased(CefRefPtr<CefBrowser> browser,
                                 CefRefPtr<CefFrame> frame,
                                 CefRefPtr<CefV8Context> context) {

appshell/client_app.h

@@ -102,6 +102,15 @@ class ClientApp : public CefApp,
   }
   virtual CefRefPtr<CefRenderProcessHandler> GetRenderProcessHandler()
       OVERRIDE { return this; }
+
+  virtual CefRefPtr<CefBrowserProcessHandler> GetBrowserProcessHandler()
+	  OVERRIDE { return this; }
+  virtual void OnBeforeCommandLineProcessing(
+	  const CefString& process_type,
+	  CefRefPtr<CefCommandLine> command_line);
+
+  virtual void OnBeforeChildProcessLaunch(
+	  CefRefPtr<CefCommandLine> command_line);
 
   // CefRenderProcessHandler methods.
   virtual void OnWebKitInitialized() OVERRIDE;