platform_util::OpenItem fixes

chrome/browser/platform_util.h

Index: chrome/browser/platform_util.h
===================================================================
--- chrome/browser/platform_util.h	(revision 108954)
+++ chrome/browser/platform_util.h	(working copy)
@@ -17,9 +17,11 @@
 namespace platform_util {
 
 // Show the given file in a file manager. If possible, select the file.
+// Must be called from the UI thread.

[Mark Mentovai, 2011/11/09 14:22:50]

This doesn’t seem to be true.

It‘s definitely true of the Mac implementation. However, some of the other
implementations allow it to be called from any thread.

Perhaps those implementations could be refactored slightly so that the work that
needs to be done on the file thread is moved to a separate
(anonymous-namespaced?) helper function. Then, ShowItemInFolder and OpenItem can
DCHECK that they’re on the UI thread and post to the file thread; the helpers
can DCHECK that they’re on the file thread and do the work.

That seems substantially cleaner than having some platforms recycle
ShowItemInFolder and OpenItem for different purposes depending on which thread
they’re on, and having them implement different logic for checking thread
correctness and dealing with being called on an unexpected thread.

[achuithb, 2011/11/09 20:21:36]

Done.

 void ShowItemInFolder(const FilePath& full_path);
 
 // Open the given file in the desktop's default manner.
+// Must be called from the UI thread.
 void OpenItem(const FilePath& full_path);
 
 // Open the given external protocol URL in the desktop's default manner.