Add a policy to re-enable deprecated web platform features.

chrome/browser/policy/configuration_policy_handler_list_factory.cc

Index: chrome/browser/policy/configuration_policy_handler_list_factory.cc
diff --git a/chrome/browser/policy/configuration_policy_handler_list_factory.cc b/chrome/browser/policy/configuration_policy_handler_list_factory.cc
index d8e3239a54e12e733c1a9bb070d8f917febf6a88..a9536abd463c2692eff4b1b07bfe437f781f3ceb 100644
--- a/chrome/browser/policy/configuration_policy_handler_list_factory.cc
+++ b/chrome/browser/policy/configuration_policy_handler_list_factory.cc
@@ -34,6 +34,7 @@
 #include "chrome/browser/policy/javascript_policy_handler.h"
 #include "chrome/browser/sessions/restore_on_startup_policy_handler.h"
 #include "chrome/browser/sync/sync_policy_handler.h"
+#include "content/public/common/renderer_preferences.h"
 #include "extensions/browser/pref_names.h"
 #include "extensions/common/manifest.h"
 #endif
@@ -491,6 +492,13 @@ StringToIntEnumListPolicyHandler::MappingEntry kExtensionAllowedTypesMap[] = {
   { "legacy_packaged_app", extensions::Manifest::TYPE_LEGACY_PACKAGED_APP },
   { "platform_app", extensions::Manifest::TYPE_PLATFORM_APP },
 };
+
+// Maps feature tags as specified in policy to the corresponding enum value.
+StringToIntEnumListPolicyHandler::MappingEntry

[Andrew T Wilson (Slow), 2014/05/08 11:32:45]

BTW, should add a TODO + a crbug entry to remove this once the deprecation date
is passed.

[Mattias Nissler (ping if slow), 2014/05/09 16:38:27]

Adam, would you like to track this as part of http://crbug.com/345831 or would
you prefer a separate bug?

+    kEnableDeprecatedWebPlatformFeaturesMap[] = {
+  {"ShowModalDialog",

[Mattias Nissler (ping if slow), 2014/05/06 14:31:15]

We should talk some more about the naming - do we want to explicitly include the
intended removal date into the tag name?

We could as well put a hard time limit here, and we'd automatically stop
supporting the feature once we're past that time. That would have the benefit of
avoiding the negative effect of people staying on old versions just because
those still support the deprecation policy - the feature would self destruct at
a prescribed point in time. WDYT?

[Andrew T Wilson (Slow), 2014/05/08 11:32:45]

If people are going to stay on old versions to keep deprecated features, then
they'll just stick to a version that is pre-deprecation.

That said, I like the idea of hardcoding a deprecation date, so I'm OK with
doing that.

Also, I think we should absolutely come up with some standard for naming that
includes the final deprecation date - I'd suggest "XXXXUntilDate" (for example:
"ShowModalDialogUntilDec2014").

[Mattias Nissler (ping if slow), 2014/05/09 16:38:27]

That's certainly a risk, but they'd have to retain an old copy of the installer
and wipe Chrome state for all users etc., so that's pretty painful...

In the end, we need to decide which option we think is less risky overall. I
tend to lean towards timed self-destruct. What do others think?
Okay, how about <FEATURE>_Until_<yyyymmdd>? If we do self-destruct, we should
specify the day IMHO.

+   content::RENDERER_PREFERENCES_DEPRECATED_FEATURE_SHOW_MODAL_DIALOG},
+};
 #endif  // !defined(OS_IOS)
 
 }  // namespace
@@ -561,6 +569,13 @@ scoped_ptr<ConfigurationPolicyHandlerList> BuildHandlerList(
           extensions::pref_names::kAllowedTypes,
           kExtensionAllowedTypesMap,
           kExtensionAllowedTypesMap + arraysize(kExtensionAllowedTypesMap))));
+  handlers->AddHandler(make_scoped_ptr<ConfigurationPolicyHandler>(
+      new StringToIntEnumListPolicyHandler(
+          key::kEnableDeprecatedWebPlatformFeatures,
+          prefs::kEnableDeprecatedWebPlatformFeatures,
+          kEnableDeprecatedWebPlatformFeaturesMap,
+          kEnableDeprecatedWebPlatformFeaturesMap +
+              arraysize(kEnableDeprecatedWebPlatformFeaturesMap))));
 #endif  // !defined(OS_IOS)
 
 #if !defined(OS_CHROMEOS) && !defined(OS_ANDROID) && !defined(OS_IOS)