Issue #1620 - Use Intrinsic Aspect Ratio for Images

https://bugzilla.mozilla.org/show_bug.cgi?id=1547231
https://bugzilla.mozilla.org/show_bug.cgi?id=1559094
https://bugzilla.mozilla.org/show_bug.cgi?id=1633434
https://bugzilla.mozilla.org/show_bug.cgi?id=1565690
https://bugzilla.mozilla.org/show_bug.cgi?id=1602047

Make use of Aspect Ratios in Image frames before Images are loaded.
- Check for width and height HTML properties and create a ratio with them.
- Overwrite HTML size values with actual image dimensions on load.
- Collapse any frames with srcless images.

Comments:
dom/html/nsGenericHTMLElement.cpp:1483
layout/generic/nsImageFrame.cpp:289

layout/style/nsStyleStruct.cpp

@@ -1408,6 +1408,7 @@ nsStylePosition::nsStylePosition(StyleStructContext aContext)
   , mGridAutoColumnsMax(eStyleUnit_Auto)
   , mGridAutoRowsMin(eStyleUnit_Auto)
   , mGridAutoRowsMax(eStyleUnit_Auto)
+  , mAspectRatio(0.0f)
   , mGridAutoFlow(NS_STYLE_GRID_AUTO_FLOW_ROW)
   , mBoxSizing(StyleBoxSizing::Content)
   , mAlignContent(NS_STYLE_ALIGN_NORMAL)
@@ -1466,6 +1467,7 @@ nsStylePosition::nsStylePosition(const nsStylePosition& aSource)
   , mGridAutoColumnsMax(aSource.mGridAutoColumnsMax)
   , mGridAutoRowsMin(aSource.mGridAutoRowsMin)
   , mGridAutoRowsMax(aSource.mGridAutoRowsMax)
+  , mAspectRatio(aSource.mAspectRatio)
   , mGridAutoFlow(aSource.mGridAutoFlow)
   , mBoxSizing(aSource.mBoxSizing)
   , mAlignContent(aSource.mAlignContent)
@@ -1636,6 +1638,11 @@ nsStylePosition::CalcDifference(const nsStylePosition& aNewData,
     if (isVertical ? heightChanged : widthChanged) {
       hint |= nsChangeHint_ReflowHintsForISizeChange;
     }
+
+    if (mAspectRatio != aNewData.mAspectRatio) {
+      hint |= nsChangeHint_ReflowHintsForISizeChange |
+              nsChangeHint_ReflowHintsForBSizeChange;
+    }
   } else {
     if (widthChanged || heightChanged) {
       hint |= nsChangeHint_NeutralChange;