Bug 1674863 Part 2 - Use strong types to define fallback intrinsic width, height, and size. r=emilio

Differential Revision: https://phabricator.services.mozilla.com/D95578

gfx/2d/BaseCoord.h

@@ -30,7 +30,7 @@ struct BaseCoord {
   // Note that '=' isn't defined so we'll get the
   // compiler generated default assignment operator
 
-  operator T() const { return value; }
+  constexpr operator T() const { return value; }
 
   friend bool operator==(Sub aA, Sub aB) { return aA.value == aB.value; }
   friend bool operator!=(Sub aA, Sub aB) { return aA.value != aB.value; }

layout/base/LayoutConstants.h

@@ -11,6 +11,7 @@
 
 #include "mozilla/EnumSet.h"
 #include "nsSize.h"  // for NS_MAXSIZE
+#include "Units.h"
 
 /**
  * Constant used to indicate an unconstrained size.
@@ -29,12 +30,6 @@
 
 #define NS_INTRINSIC_ISIZE_UNKNOWN nscoord_MIN
 
-// The fallback size of width is 300px and the aspect-ratio is 2:1, based on the
-// spec definition in CSS2 section 10.3.2:
-// https://drafts.csswg.org/css2/visudet.html#inline-replaced-width
-#define REPLACED_ELEM_FALLBACK_PX_WIDTH 300
-#define REPLACED_ELEM_FALLBACK_PX_HEIGHT 150
-
 namespace mozilla {
 
 /**
@@ -84,6 +79,17 @@ enum class ComputeSizeFlag : uint8_t {
 };
 using ComputeSizeFlags = mozilla::EnumSet<ComputeSizeFlag>;
 
+/**
+ * The fallback size of width is 300px and the aspect-ratio is 2:1, based on
+ * CSS2 section 10.3.2 and CSS Sizing Level 3 section 5.1:
+ * https://drafts.csswg.org/css2/visudet.html#inline-replaced-width
+ * https://drafts.csswg.org/css-sizing-3/#intrinsic-sizes
+ */
+inline constexpr CSSIntCoord kFallbackIntrinsicWidthInPixels(300);
+inline constexpr CSSIntCoord kFallbackIntrinsicHeightInPixels(150);
+inline constexpr CSSIntSize kFallbackIntrinsicSizeInPixels(
+    kFallbackIntrinsicWidthInPixels, kFallbackIntrinsicHeightInPixels);
+
 /**
  * This is used in some nsLayoutUtils functions.
  * Declared here so that fewer files need to include nsLayoutUtils.h.

layout/generic/nsSubDocumentFrame.cpp

@@ -634,11 +634,8 @@ IntrinsicSize nsSubDocumentFrame::GetIntrinsicSize() {
     return {};  // XUL <iframe> and <browser> have no useful intrinsic size
   }
 
-  // We must be an HTML <iframe>.  Default to size of
-  // REPLACED_ELEM_FALLBACK_PX_WIDTH x REPLACED_ELEM_FALLBACK_PX_HEIGHT (i.e.
-  // 300px x 150px), for IE compat (and per CSS2.1 draft)
-  return IntrinsicSize(CSSPixel::ToAppUnits(REPLACED_ELEM_FALLBACK_PX_WIDTH),
-                       CSSPixel::ToAppUnits(REPLACED_ELEM_FALLBACK_PX_HEIGHT));
+  // We must be an HTML <iframe>. Return fallback size.
+  return IntrinsicSize(CSSPixel::ToAppUnits(kFallbackIntrinsicSizeInPixels));
 }
 
 /* virtual */

layout/generic/nsVideoFrame.cpp

@@ -648,8 +648,7 @@ AspectRatio nsVideoFrame::GetIntrinsicRatio() const {
     }
   }
 
-  return AspectRatio::FromSize(REPLACED_ELEM_FALLBACK_PX_WIDTH,
-                               REPLACED_ELEM_FALLBACK_PX_HEIGHT);
+  return AspectRatio::FromSize(kFallbackIntrinsicSizeInPixels);
 }
 
 bool nsVideoFrame::ShouldDisplayPoster() const {
@@ -692,8 +691,7 @@ nsSize nsVideoFrame::GetVideoIntrinsicSize(gfxContext* aRenderingContext) {
     }
   }
 
-  return CSSPixel::ToAppUnits(CSSIntSize(REPLACED_ELEM_FALLBACK_PX_WIDTH,
-                                         REPLACED_ELEM_FALLBACK_PX_HEIGHT));
+  return CSSPixel::ToAppUnits(kFallbackIntrinsicSizeInPixels);
 }
 
 void nsVideoFrame::UpdatePosterSource(bool aNotify) {