Bug 1587973 - Part 1: Use CSS pixels or device pixels in ResizeObserverSize. r=emilio

We will introduce device-pixel-content-box, which is in device-pixel
domain. Therefore, we convert the app units into CSS/device pixel when creating
ResizeObserverSize.

Differential Revision: https://phabricator.services.mozilla.com/D121016

dom/base/ResizeObserver.cpp

@@ -370,7 +370,8 @@ void ResizeObserverEntry::GetContentBoxSize(
 void ResizeObserverEntry::SetBorderBoxSize(const nsSize& aSize) {
   nsIFrame* frame = mTarget->GetPrimaryFrame();
   const WritingMode wm = frame ? frame->GetWritingMode() : WritingMode();
-  mBorderBoxSize = new ResizeObserverSize(this, aSize, wm);
+  mBorderBoxSize = new ResizeObserverSize(
+      this, CSSSize::FromAppUnits(aSize).ToUnknownSize(), wm);
 }
 
 void ResizeObserverEntry::SetContentRectAndSize(const nsSize& aSize) {
@@ -387,7 +388,8 @@ void ResizeObserverEntry::SetContentRectAndSize(const nsSize& aSize) {
 
   // 2. Update mContentBoxSize.
   const WritingMode wm = frame ? frame->GetWritingMode() : WritingMode();
-  mContentBoxSize = new ResizeObserverSize(this, aSize, wm);
+  mContentBoxSize = new ResizeObserverSize(
+      this, CSSSize::FromAppUnits(aSize).ToUnknownSize(), wm);
 }
 
 NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(ResizeObserverSize, mOwner)

dom/base/ResizeObserver.h

@@ -7,6 +7,7 @@
 #ifndef mozilla_dom_ResizeObserver_h
 #define mozilla_dom_ResizeObserver_h
 
+#include "gfxPoint.h"
 #include "js/TypeDecls.h"
 #include "mozilla/AppUnits.h"
 #include "mozilla/Attributes.h"
@@ -231,11 +232,9 @@ class ResizeObserverSize final : public nsISupports, public nsWrapperCache {
   NS_DECL_CYCLE_COLLECTING_ISUPPORTS
   NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(ResizeObserverSize)
 
-  // Note: the unit of |aSize| is app unit, and we convert it into css pixel in
-  // the public JS APIs.
-  ResizeObserverSize(nsISupports* aOwner, const nsSize& aSize,
+  ResizeObserverSize(nsISupports* aOwner, const gfx::Size& aSize,
                      const WritingMode aWM)
-      : mOwner(aOwner), mSize(aWM, aSize), mWM(aWM) {
+      : mOwner(aOwner), mSize(aSize), mWM(aWM) {
     MOZ_ASSERT(mOwner, "Need a non-null owner");
   }
 
@@ -247,18 +246,22 @@ class ResizeObserverSize final : public nsISupports, public nsWrapperCache {
   }
 
   double InlineSize() const {
-    return NSAppUnitsToDoublePixels(mSize.ISize(mWM), AppUnitsPerCSSPixel());
+    return mWM.IsVertical() ? mSize.Height() : mSize.Width();
   }
 
   double BlockSize() const {
-    return NSAppUnitsToDoublePixels(mSize.BSize(mWM), AppUnitsPerCSSPixel());
+    return mWM.IsVertical() ? mSize.Width() : mSize.Height();
   }
 
  protected:
   ~ResizeObserverSize() = default;
 
   nsCOMPtr<nsISupports> mOwner;
-  const LogicalSize mSize;
+  // The physical size value:
+  // 1. content-box/border-box: in CSS pixels.
+  // 2. device-pixel-content-box: in device pixels.
+  const gfx::Size mSize;
+  // The writing mode of |mSize|.
   const WritingMode mWM;
 };