Create direct write font proxy classes and unit tests.

content/common/font_warmup_win.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_COMMON_FONT_WARMUP_WIN_H_
 #define CONTENT_COMMON_FONT_WARMUP_WIN_H_
 
 #include "base/files/file_path.h"
 #include "content/common/content_export.h"
 
@@ skipping 32 matching lines @@
 // Testing method to reset the table of emulated GDI handles.
 CONTENT_EXPORT void ResetEmulatedGdiHandlesForTesting();
 
 // Sets the pre-sandbox warmup font manager directly. This should only be used
 // for testing the implementation.
 CONTENT_EXPORT void SetPreSandboxWarmupFontMgrForTesting(SkFontMgr* fontmgr);
 
 // Warmup the direct write font manager for content processes.
 CONTENT_EXPORT void WarmupDirectWrite();
 
+// Directwrite connects to the font cache service to retrieve information about
+// fonts installed on the system etc. This works well outside the sandbox and
+// within the sandbox as long as the lpc connection maintained by the current
+// process with the font cache service remains valid. It appears that there
+// are cases when this connection is dropped after which directwrite is unable
+// to connect to the font cache service which causes problems with characters
+// disappearing.
+// Directwrite has fallback code to enumerate fonts if it is unable to connect
+// to the font cache service. We need to intercept the following APIs to
+// ensure that it does not connect to the font cache service.
+// NtALpcConnectPort
+// OpenSCManagerW
+// OpenServiceW
+// StartServiceW
+// CloseServiceHandle.
+// These are all IAT patched.
+CONTENT_EXPORT void PatchServiceManagerCalls();
+
 }  // namespace content
 
 #endif  // CONTENT_COMMON_FONT_WARMUP_WIN_H_