[chromedriver] Use disable-extensions-except on Windows and Mac.

chrome/test/chromedriver/chrome_launcher.cc

Index: chrome/test/chromedriver/chrome_launcher.cc
diff --git a/chrome/test/chromedriver/chrome_launcher.cc b/chrome/test/chromedriver/chrome_launcher.cc
index 567637e8b6466ca68c2d386376f7008012edd8ed..1592c2913c813c10936865934ba31f80edf66884 100644
--- a/chrome/test/chromedriver/chrome_launcher.cc
+++ b/chrome/test/chromedriver/chrome_launcher.cc
@@ -775,24 +775,25 @@ Status ProcessExtensions(const std::vector<std::string>& extensions,
     Status status = UnpackAutomationExtension(temp_dir, &automation_extension);
     if (status.IsError())
       return status;
-#if defined(OS_WIN) || defined(OS_MACOSX)
-    // On Chrome for Windows and Mac, a "Disable developer mode extensions"
-    // dialog appears for the automation extension. Suppress this by loading
-    // it as a component extension.
-    UpdateExtensionSwitch(switches, "load-component-extension",
-                          automation_extension.value());
-#else
     if (switches->HasSwitch("disable-extensions")) {
-      // For Chrome 56 and earlier:
-      UpdateExtensionSwitch(switches, "load-component-extension",
-                            automation_extension.value());
-      // For Chrome 57 and later:
       UpdateExtensionSwitch(switches, "disable-extensions-except",
                             automation_extension.value());
+      // TODO(samuong): Stop using --load-component-extension when ChromeDriver
+      // stops supporting Chrome 56. For backwards compatibility, Chrome 57 and
+      // 58 interprets --load-component-extension as --load-extension.
+      UpdateExtensionSwitch(switches, "load-component-extension",
+                            automation_extension.value());
     } else {
+#if defined(OS_WIN) || defined(OS_MACOSX)
+      // On Chrome 56 for Windows and Mac, a "Disable developer
+      // mode extensions" dialog appears for the automation extension. Suppress
+      // this by loading it as a component extension.
+      UpdateExtensionSwitch(switches, "load-component-extension",
+                            automation_extension.value());
+#else
       extension_paths.push_back(automation_extension.value());
-    }
 #endif
+    }
   }
 
   if (extension_paths.size()) {