Issue #1619 - Convert Intrinsic Ratio to Float

https://bugzilla.mozilla.org/show_bug.cgi?id=1547792

Aspect Ratio handling simplified by using floating point integers:
- Multiplication of value (or inverse value) to a known side for Scaling
- No unequal equal values such as "4/3" vs "8/6" vs "20/15"
- Truly "Empty" aspect ratios, even if one dimension is not 0

image/DynamicImage.cpp

@@ -136,10 +136,10 @@ DynamicImage::GetIntrinsicSize(nsSize* aSize)
 }
 
 NS_IMETHODIMP
-DynamicImage::GetIntrinsicRatio(nsSize* aSize)
+DynamicImage::GetIntrinsicRatio(AspectRatio* aRatio)
 {
-  IntSize intSize(mDrawable->Size());
-  *aSize = nsSize(intSize.width, intSize.height);
+  auto size = mDrawable->Size();
+  *aRatio = AspectRatio::FromSize(size);
   return NS_OK;
 }