Make chrome_plugin_host.cc and chrome_plugin_util.cc compile on Posix.

chrome/common/temp_scaffolding_stubs.h

Index: chrome/common/temp_scaffolding_stubs.h
===================================================================
--- chrome/common/temp_scaffolding_stubs.h	(revision 10402)
+++ chrome/common/temp_scaffolding_stubs.h	(working copy)
@@ -629,6 +629,16 @@
                           IPC::Message*, WebContents*) { }
 };
 
+class HtmlDialogContents {
+ public:
+  struct HtmlDialogParams {
+    GURL url;
+    int width;
+    int height;
+    std::string json_input;
+  };
+};
+
 class CharacterEncoding {
  public:
   static std::wstring GetCanonicalEncodingNameByAliasName(