Fix SkTFits in to work properly with signed/unsigned mixtures.

src/utils/win/SkDWriteFontFileStream.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkTypes.h"
 #include "SkDWriteFontFileStream.h"
 #include "SkHRESULT.h"
 #include "SkTemplates.h"
+#include "SkTFitsIn.h"
 #include "SkTScopedComPtr.h"
 
 #include <dwrite.h>
-#include <limits>
 
 ///////////////////////////////////////////////////////////////////////////////
 //  SkIDWriteFontFileStream
 
 SkDWriteFontFileStream::SkDWriteFontFileStream(IDWriteFontFileStream* fontFileStream)
     : fFontFileStream(SkRefComPtr(fontFileStream))
     , fPos(0)
     , fLockedMemory(NULL)
     , fFragmentLock(NULL) {
 }
@@ skipping 150 matching lines @@
 {
     // The loader is responsible for doing a bounds check.
     UINT64 fileSize;
     this->GetFileSize(&fileSize);
     if (fileOffset > fileSize || fragmentSize > fileSize - fileOffset) {
         *fragmentStart = NULL;
         *fragmentContext = NULL;
         return E_FAIL;
     }
 
-    if (fileOffset + fragmentSize > (std::numeric_limits<size_t>::max)()) {
+    if (!SkTFitsIn<size_t>(fileOffset + fragmentSize)) {
         return E_FAIL;
     }
 
     const void* data = fStream->getMemoryBase();
     if (NULL != data) {
         *fragmentStart = static_cast<BYTE const*>(data) + static_cast<size_t>(fileOffset);
         *fragmentContext = NULL;
 
     } else {
         //May be called from multiple threads.
@@ skipping 26 matching lines @@
 HRESULT STDMETHODCALLTYPE SkDWriteFontFileStreamWrapper::GetFileSize(UINT64* fileSize) {
     *fileSize = fStream->getLength();
     return S_OK;
 }
 
 HRESULT STDMETHODCALLTYPE SkDWriteFontFileStreamWrapper::GetLastWriteTime(UINT64* lastWriteTime) {
     // The concept of last write time does not apply to this loader.
     *lastWriteTime = 0;
     return E_NOTIMPL;
 }