Step 2 in porting disk cache to using FilePath.

base/platform_file.h

Index: base/platform_file.h
diff --git a/base/platform_file.h b/base/platform_file.h
index 5d8426254d6e7d2e94edfb4e9316e374cdad7ff6..0dbf4e4aa7cdce1e623f023c0ba0e762049fa604 100644
--- a/base/platform_file.h
+++ b/base/platform_file.h
@@ -12,6 +12,8 @@
 
 #include <string>
 
+class FilePath;
+
 namespace base {
 
 #if defined(OS_WIN)
@@ -40,6 +42,10 @@ enum PlatformFileFlags {
 // Creates or opens the given file. If PLATFORM_FILE_OPEN_ALWAYS is used, and
 // |created| is provided, |created| will be set to true if the file was created
 // or to false in case the file was just opened.
+PlatformFile CreatePlatformFile(const FilePath& name,
+                                int flags,
+                                bool* created);
+// Deprecated.
 PlatformFile CreatePlatformFile(const std::wstring& name,
                                 int flags,
                                 bool* created);