FreeType uses unsigned int, Skia uses int.

Fix warning about assert which compared signed and unsigned.

Review URL: https://codereview.chromium.org/956623004
diff --git a/src/ports/SkFontHost_FreeType_common.cpp b/src/ports/SkFontHost_FreeType_common.cpp
index bd3cddf..e03599f 100644
--- a/src/ports/SkFontHost_FreeType_common.cpp
+++ b/src/ports/SkFontHost_FreeType_common.cpp
@@ -177,8 +177,8 @@
  *  TODO: All of these N need to be Y or otherwise ruled out.
  */
 static void copyFTBitmap(const FT_Bitmap& srcFTBitmap, SkMask& dstMask) {
-    SkASSERT(dstMask.fBounds.width() == srcFTBitmap.width);
-    SkASSERT(dstMask.fBounds.height() == srcFTBitmap.rows);
+    SkASSERT(dstMask.fBounds.width() == static_cast<int>(srcFTBitmap.width));
+    SkASSERT(dstMask.fBounds.height() == static_cast<int>(srcFTBitmap.rows));
 
     const uint8_t* src = reinterpret_cast<const uint8_t*>(srcFTBitmap.buffer);
     const FT_Pixel_Mode srcFormat = static_cast<FT_Pixel_Mode>(srcFTBitmap.pixel_mode);