use SkFourByteTag to squelch warnings

    [173/2069] compile ../src/ports/SkTypeface_mac_ct.cpp
    ../src/ports/SkTypeface_mac_ct.cpp:649:29: warning: multi-character character constant [-Wfour-char-constants]
        if (!this->getTableSize('glyf') || !this->getTableSize('loca')) {
                                ^
    ../src/ports/SkTypeface_mac_ct.cpp:649:60: warning: multi-character character constant [-Wfour-char-constants]
        if (!this->getTableSize('glyf') || !this->getTableSize('loca')) {
                                                               ^

Change-Id: I9dc691be285fe0e144aaabe4b81e6bc775564423
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/333483
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
Auto-Submit: Mike Klein <mtklein@google.com>

Author: Mike Klein

src/ports/SkTypeface_mac_ct.cpp

@@ -646,7 +646,9 @@ std::unique_ptr<SkAdvancedTypefaceMetrics> SkTypeface_Mac::onGetAdvancedMetrics(
     // fonts always have both glyf and loca tables. At the least, this is what
     // sfntly needs to subset the font. CTFontCopyAttribute() does not always
     // succeed in determining this directly.
-    if (!this->getTableSize('glyf') || !this->getTableSize('loca')) {
+    if (!this->getTableSize(SkSetFourByteTag('g','l','y','f')) ||
+        !this->getTableSize(SkSetFourByteTag('l','o','c','a')))
+    {
         return info;
     }