Bug 1674868 Part 1: Prevent memory leaks in NativeFontResourceMac::Create when font creation fails. r=jrmuizel

Any CT "Create" method returns an owned object. This ensures that owned
objects are deallocated when the font fails to be crated. It also prevents
unused font data from being entered into the font data set (where it would
never be deallocated).

Differential Revision: https://phabricator.services.mozilla.com/D96121

gfx/2d/NativeFontResourceMac.cpp

@@ -70,17 +70,16 @@ already_AddRefed<NativeFontResourceMac> NativeFontResourceMac::Create(
                                 nullptr, nullptr,  nullptr, FontDataDeallocate,
                                 nullptr};
   CFAllocatorRef allocator = CFAllocatorCreate(kCFAllocatorDefault, &context);
+
+  // We create a CFDataRef here that we'l hold until we've determined that we
+  // have a valid font. If and only if we can create a font from the data,
+  // we'll store the font data in our map. Whether or not the font is valid,
+  // we'll later release this CFDataRef.
   CFDataRef data = CFDataCreateWithBytesNoCopy(kCFAllocatorDefault, fontData,
                                                aDataLength, allocator);
 
-  {
-    auto set = sWeakFontDataSet.Lock();
-    set->insert(fontData);
-  }
-
   CTFontDescriptorRef ctFontDesc =
       CTFontManagerCreateFontDescriptorFromData(data);
-  CFRelease(data);
 
   // creating the CGFontRef via the CTFont avoids the data being held alive
   // in a cache.
@@ -93,9 +92,19 @@ already_AddRefed<NativeFontResourceMac> NativeFontResourceMac::Create(
   CFRelease(ctFont);
 
   if (!fontRef) {
+    // Not a valid font; release the structures we've been holding.
+    CFRelease(data);
+    CFRelease(ctFontDesc);
     return nullptr;
   }
 
+  {
+    auto set = sWeakFontDataSet.Lock();
+    set->insert(fontData);
+  }
+  // It's now safe to release our CFDataRef.
+  CFRelease(data);
+
   // passes ownership of fontRef to the NativeFontResourceMac instance
   RefPtr<NativeFontResourceMac> fontResource =
       new NativeFontResourceMac(ctFontDesc, fontRef, aDataLength);