Extract ProcessManager from ExtensionSystem.

This change removes ProcessManager's //chrome dependency because while
ProcessManager and ExtensionSystem are in //extensions the
ExtensionSystemFactory is in //chrome. This allows a service in
//extensions to declare a dependency on the ProcessManager's factory
directly.

Most of this patch is changing,
extensions::ExtensionSystem::Get(profile_)->process_manager() to, extensions::ProcessManager::Get(profile_).

BUG=
[email protected]

Review URL: https://codereview.chromium.org/671763002

Cr-Commit-Position: refs/heads/master@{#301636}
diff --git a/chrome/browser/extensions/extension_service.cc b/chrome/browser/extensions/extension_service.cc
index 8223ed1..7636dfe7 100644
--- a/chrome/browser/extensions/extension_service.cc
+++ b/chrome/browser/extensions/extension_service.cc
@@ -598,7 +598,8 @@
     // the inspector and hang onto a cookie for it, so that we can reattach
     // later.
     // TODO(yoz): this is not incognito-safe!
-    extensions::ProcessManager* manager = system_->process_manager();
+    extensions::ProcessManager* manager =
+        extensions::ProcessManager::Get(profile_);
     extensions::ExtensionHost* host =
         manager->GetBackgroundHostForExtension(extension_id);
     if (host && DevToolsAgentHost::HasFor(host->host_contents())) {