Add a BrowserThread::DCheckCurrentlyOn function.

content/public/browser/browser_thread.h

Index: content/public/browser/browser_thread.h
diff --git a/content/public/browser/browser_thread.h b/content/public/browser/browser_thread.h
index 55cb62b22355d339822414f06874d2bd2695590f..47d3c1d90a7597693c506bb5bbfe542f7d795558 100644
--- a/content/public/browser/browser_thread.h
+++ b/content/public/browser/browser_thread.h
@@ -10,15 +10,12 @@
 #include "base/basictypes.h"
 #include "base/callback.h"
 #include "base/location.h"
+#include "base/logging.h"
 #include "base/message_loop/message_loop_proxy.h"
 #include "base/task_runner_util.h"
 #include "base/time/time.h"
 #include "content/common/content_export.h"
 
-#if defined(UNIT_TEST)
-#include "base/logging.h"
-#endif  // UNIT_TEST
-
 namespace base {
 class MessageLoop;
 class SequencedWorkerPool;
@@ -188,7 +185,7 @@ class CONTENT_EXPORT BrowserThread {
   static bool IsThreadInitialized(ID identifier);
 
   // Callable on any thread.  Returns whether you're currently on a particular
-  // thread.
+  // thread.  To DCHECK this, see the DCHECK_CURRENTLY_ON() macro below.
   static bool CurrentlyOn(ID identifier);
 
   // Callable on any thread.  Returns whether the threads message loop is valid.
@@ -266,6 +263,9 @@ class CONTENT_EXPORT BrowserThread {
   struct DeleteOnFileThread : public DeleteOnThread<FILE> { };
   struct DeleteOnDBThread : public DeleteOnThread<DB> { };
 
+  // Returns an appropriate error message for when DCHECK_CURRENTLY_ON() fails.
+  static std::string GetDCheckCurrentlyOnErrorMessage(ID expected);
+
  private:
   friend class BrowserThreadImpl;
 
@@ -273,6 +273,11 @@ class CONTENT_EXPORT BrowserThread {
   DISALLOW_COPY_AND_ASSIGN(BrowserThread);
 };
 
+#define DCHECK_CURRENTLY_ON(thread_identifier)                      \

[Jói, 2014/03/11 08:41:25]

nit: This would be more discoverable if placed at the top of this header. A
sentence of documentation would also help.

[Jeffrey Yasskin, 2014/03/11 19:11:22]

SG. Done, thanks.

+  (DCHECK(::content::BrowserThread::CurrentlyOn(thread_identifier)) \
+   << ::content::BrowserThread::GetDCheckCurrentlyOnErrorMessage(   \
+          thread_identifier))
+
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_BROWSER_THREAD_H_