Relanding this as the previous attempt failed due to build errors.

webkit/plugins/npapi/plugin_constants_win.h

Index: webkit/plugins/npapi/plugin_constants_win.h
===================================================================
--- webkit/plugins/npapi/plugin_constants_win.h	(revision 200310)
+++ webkit/plugins/npapi/plugin_constants_win.h	(working copy)
@@ -6,7 +6,6 @@
 #define WEBKIT_PLUGINS_NPAPI_PLUGIN_CONSTANTS_WIN_H_
 
 #include "base/string16.h"
-#include "webkit/plugins/webkit_plugins_export.h"
 
 #if !defined(OS_WIN)
 #error "Windows-only header"
@@ -21,17 +20,17 @@
 // The name of the window class name for the wrapper HWND around the actual
 // plugin window that's used when running in multi-process mode.  This window
 // is created on the browser UI thread.
-WEBKIT_PLUGINS_EXPORT extern const char16 kWrapperNativeWindowClassName[];
+extern const char16 kWrapperNativeWindowClassName[];
 
 // The name of the custom window message that the browser uses to tell the
 // plugin process to paint a window.
-WEBKIT_PLUGINS_EXPORT extern const char16 kPaintMessageName[];
+extern const char16 kPaintMessageName[];
 
 // The name of the registry key which NPAPI plugins update on installation.
-WEBKIT_PLUGINS_EXPORT extern const char16 kRegistryMozillaPlugins[];
+extern const char16 kRegistryMozillaPlugins[];
 
 extern const char16 kMozillaActiveXPlugin[];
-WEBKIT_PLUGINS_EXPORT extern const char16 kNewWMPPlugin[];
+extern const char16 kNewWMPPlugin[];
 extern const char16 kOldWMPPlugin[];
 extern const char16 kYahooApplicationStatePlugin[];
 extern const char16 kWanWangProtocolHandlerPlugin[];