Add an escape hatch for loading legacy manifests

This patch adds a --allow-legacy-extension-manifests command line switch that
lets folks load extenions with old manifest_verions even if they would
otherwise be forbidden.

This escape hatch will help ease the transition to modern manifests, both for
us and for extension developers.  (We plan to use this switch internally to
avoid converting some test data to modern manifests.)

BUG=62897
Review URL: http://codereview.chromium.org/8776059

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@112786 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/chrome_content_browser_client.cc

@@ -564,6 +564,7 @@ void ChromeContentBrowserClient::AppendExtraCommandLineSwitches(
 
     static const char* const kSwitchNames[] = {
       switches::kAllowHTTPBackgroundPage,
+      switches::kAllowLegacyExtensionManifests,
       switches::kAllowScriptingGallery,
       switches::kAppsCheckoutURL,
       switches::kAppsGalleryURL,

chrome/common/chrome_switches.cc

@@ -29,6 +29,11 @@ const char kAllowFileAccess[]               = "allow-file-access";
 // Allows non-https URL for background_page for hosted apps.
 const char kAllowHTTPBackgroundPage[]       = "allow-http-background-page";
 
+// Allows the browser to load extensions that lack a modern manifest when that
+// would otherwise be forbidden.
+const char kAllowLegacyExtensionManifests[]
+    = "allow-legacy-extension-manifests";
+
 // Don't block outdated plugins.
 const char kAllowOutdatedPlugins[]          = "allow-outdated-plugins";
 

chrome/common/chrome_switches.h

@@ -26,6 +26,7 @@ namespace switches {
 extern const char kAllowCrossOriginAuthPrompt[];
 extern const char kAllowFileAccess[];
 extern const char kAllowHTTPBackgroundPage[];
+extern const char kAllowLegacyExtensionManifests[];
 extern const char kAllowOutdatedPlugins[];
 extern const char kAllowRunningInsecureContent[];
 extern const char kAllowScriptingGallery[];

chrome/common/extensions/extension.cc

@@ -1413,7 +1413,9 @@ bool Extension::InitFromValue(extensions::Manifest* manifest, int flags,
   }
 
   if (flags & REQUIRE_MODERN_MANIFEST_VERSION &&
-      manifest_version() < kModernManifestVersion) {
+      manifest_version() < kModernManifestVersion &&
+      !CommandLine::ForCurrentProcess()->HasSwitch(
+                switches::kAllowLegacyExtensionManifests)) {
     *error = errors::kInvalidManifestVersion;
     return false;
   }