Add TestExtensionsBrowserClient, move ProcessManagerTest to //extensions

extensions/browser/process_manager.h

Index: extensions/browser/process_manager.h
diff --git a/extensions/browser/process_manager.h b/extensions/browser/process_manager.h
index fc7bbf49045fa43ad1079e3803fe4bdd35f05da8..0ce67521235c1d64689e7df53eb713e47eb1bcf4 100644
--- a/extensions/browser/process_manager.h
+++ b/extensions/browser/process_manager.h
@@ -131,6 +131,13 @@ class ProcessManager : public content::NotificationObserver {
   void SetKeepaliveImpulseDecrementCallbackForTesting(
       const ImpulseCallbackForTesting& callback);
 
+  // Creates an incognito-context instance for tests. Tests for non-incognito
+  // contexts can just use Create() above.
+  static ProcessManager* CreateIncognitoForTesting(
+      content::BrowserContext* incognito_context,
+      content::BrowserContext* original_context,
+      ProcessManager* original_manager);
+
  protected:
   // If |context| is incognito pass the master context as |original_context|.
   // Otherwise pass the same context for both.