Clean up ifdef around FilePath creation(webkit)

Splitting from the original patch here, crrev.com/14942008
to only include 'webkit' specific changes

BUG=102853

Review URL: https://chromiumcodereview.appspot.com/14680012

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@203002 0039d316-1c4b-4281-b951-d872f2087c98

net/base/mime_util.cc

@@ -219,11 +219,8 @@ bool MimeUtil::GetMimeTypeFromExtensionHelper(
   // Finally, we scan a secondary hard-coded list to catch types that we can
   // deduce but that we also want to allow the OS to override.
 
-#if defined(OS_WIN)
-  string ext_narrow_str = WideToUTF8(ext);
-#elif defined(OS_POSIX)
-  const string& ext_narrow_str = ext;
-#endif
+  base::FilePath path_ext(ext);
+  const string ext_narrow_str = path_ext.AsUTF8Unsafe();
   const char* mime_type;
 
   mime_type = FindMimeType(primary_mappings, arraysize(primary_mappings),

webkit/plugins/npapi/plugin_stream.cc

@@ -83,11 +83,7 @@ bool PluginStream::Open(const std::string& mime_type,
   } else {
     GURL gurl(stream_.url);
 
-#if defined(OS_WIN)
-    base::FilePath path(UTF8ToWide(gurl.path()));
-#elif defined(OS_POSIX)
-    base::FilePath path(gurl.path());
-#endif
+    base::FilePath path = base::FilePath::FromUTF8Unsafe(gurl.path());
     if (net::GetMimeTypeFromFile(path, &temp_mime_type))
       char_mime_type = temp_mime_type.c_str();
   }