Add CdmService to keep track of CDMs

content/public/common/content_client.h

Index: content/public/common/content_client.h
diff --git a/content/public/common/content_client.h b/content/public/common/content_client.h
index 9d51d5ba83d4cf5a458f84137d963d39063c7c40..bb68cd876a406104a55e2f1736d6cde3e16a9109 100644
--- a/content/public/common/content_client.h
+++ b/content/public/common/content_client.h
@@ -45,6 +45,7 @@ class ContentClient;
 class ContentPluginClient;
 class ContentRendererClient;
 class ContentUtilityClient;
+struct KeySystemRegistration;
 struct PepperPluginInfo;
 
 // Setter and getter for the client.  The client should be set early, before any
@@ -86,6 +87,10 @@ class CONTENT_EXPORT ContentClient {
   virtual void AddPepperPlugins(
       std::vector<content::PepperPluginInfo>* plugins) {}
 
+  // Gives the embedder a chance to register the key system(s) it supports.
+  virtual void AddKeySystems(

[ddorwin, 2016/01/26 20:21:53]

Can we remove the ContentRendererClient method? What is the plan there?

[xhwang, 2016/01/29 07:43:06]

There's no plan to change how the key system info is populated in the render
process (chrome -> ContentRendererClient -> ContentMediaClient ->
media::KeySystems), other than we'll remove the pepper_type after we switch to
mojo.

+      std::vector<content::KeySystemRegistration>* key_systems) {}

[xhwang, 2016/01/29 07:43:06]

As chatted offline, on Linux we'll actually need to preload the CDM in
zygote_main_linux.cc, the same as how we preload pepper plugins. When we do
that, we'll have to check whether the CDM library exists. Since we already need
to do this, probably we should just go ahead and call
KeySystemService::Register() before preloading. Then PreloadCdm() can just load
all registered CDMs.

With that, we probably don't need this AddKeySystems() call anymore.

[jrummell, 2016/03/04 01:19:40]

I looked at zygote_main_linux.cc, and actually updated it to preload the CDMs.

+
   // Gives the embedder a chance to register its own standard and saveable
   // url schemes early on in the startup sequence.
   virtual void AddAdditionalSchemes(