[Fuchsia] Fix crash in the renderer in LocalFontFaceSource

LocalFontFaceSource was expecting to FontUniqueNameLookup implementation
on all platforms except Mac, but it's implemented only on Android,
Linux and Windows, which was crashing the renderer on Fuchsia.

TBR=drott@chromium.org

Bug: 948938
Change-Id: I5557a37c2cdbf2dd5a8c0a1cb08e847b31bafd00
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1549831
Commit-Queue: Sergey Ulanov <sergeyu@chromium.org>
Reviewed-by: Kevin Marshall <kmarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#647099}

third_party/blink/renderer/core/css/local_font_face_source.cc

@@ -41,13 +41,11 @@ LocalFontFaceSource::LocalFontFaceSource(CSSFontFace* css_font_face,
 LocalFontFaceSource::~LocalFontFaceSource() {}
 
 bool LocalFontFaceSource::IsLocalNonBlocking() const {
-#if defined(OS_MACOSX)
-  return true;
-#else
   FontUniqueNameLookup* unique_name_lookup =
       FontGlobalContext::Get()->GetFontUniqueNameLookup();
+  if (!unique_name_lookup)
+    return true;
   return unique_name_lookup->IsFontUniqueNameLookupReadyForSyncLookup();
-#endif
 }
 
 bool LocalFontFaceSource::IsLocalFontAvailable(

third_party/blink/renderer/platform/fonts/font_unique_name_lookup.cc

@@ -28,7 +28,6 @@ FontUniqueNameLookup::GetPlatformUniqueNameLookup() {
 #elif defined(OS_WIN)
   return std::make_unique<FontUniqueNameLookupWin>();
 #else
-  NOTREACHED();
   return nullptr;
 #endif
 }