Split BrowserThread into public API and private implementation, step 1.

Only content/ now has the ability to create BrowserThread objects,
with the exception that tests can create the
content::TestBrowserThread subclass, and (temporarily) code in chrome/
can create the DeprecatedBrowserThread subclass.

A follow-up change will make content/ take care of its own thread
creation, remove DeprecatedBrowserThread, and move all state and
non-trivial constructors from BrowserThread down to BrowserThreadImpl.

Also moved BrowserProcessSubThread into content/ namespace.  As part
of follow-up cleanup, chrome/ will stop using this class.

BUG=98716
TEST=existing

Review URL: http://codereview.chromium.org/8392042

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@107718 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/chrome/browser/extensions/file_reader_unittest.cc b/chrome/browser/extensions/file_reader_unittest.cc
index 08e5a08..d7d63c01 100644
--- a/chrome/browser/extensions/file_reader_unittest.cc
+++ b/chrome/browser/extensions/file_reader_unittest.cc
@@ -12,7 +12,7 @@
 #include "chrome/common/extensions/extension.h"
 #include "chrome/common/extensions/extension_resource.h"
 #include "chrome/common/extensions/extension_test_util.h"
-#include "content/browser/browser_thread.h"
+#include "content/test/test_browser_thread.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace {
@@ -24,7 +24,7 @@
   }
  private:
   MessageLoop message_loop_;
-  BrowserThread file_thread_;
+  content::TestBrowserThread file_thread_;
 };
 
 class Receiver {