[Mac] Move MessagePump CrAppProtocol dependency to setup.

content/common/chrome_application_mac.mm

Index: content/common/chrome_application_mac.mm
diff --git a/content/common/chrome_application_mac.mm b/content/common/chrome_application_mac.mm
index 81b341c62568f12ebd388f0324381d43e9f5af9f..5af70e9f48e45dbe7b511ab6dc0e0ff27b2fd6bf 100644
--- a/content/common/chrome_application_mac.mm
+++ b/content/common/chrome_application_mac.mm
@@ -16,10 +16,12 @@
 // some things.
 + (NSApplication*)sharedApplication {
   NSApplication* app = [super sharedApplication];
-  if (![NSApp isKindOfClass:self]) {
-    DLOG(ERROR) << "NSApp should be of type " << [[self className] UTF8String]
-                << ", not " << [[NSApp className] UTF8String];
-    DCHECK(false) << "NSApp is of wrong type";
+  if (![app conformsToProtocol:@protocol(CrAppControlProtocol)]) {
+    // TODO(shess): This is necessary until all of the references to
+    // CrApplication are removed.
+    DLOG(ERROR) << "Existing NSApp (class " << [[app className] UTF8String]
+                << ") does not conform to required protocol.";
+    NOTREACHED();
   }
   return app;
 }