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/nsCSSPropList.h

@@ -470,6 +470,17 @@ CSS_PROP_DISPLAY(
     kAppearanceKTable,
     CSS_PROP_NO_OFFSET,
     eStyleAnimType_Discrete)
+CSS_PROP_POSITION(
+    aspect-ratio,
+    aspect_ratio,
+    AspectRatio,
+    CSS_PROPERTY_INTERNAL |
+        CSS_PROPERTY_PARSE_INACCESSIBLE,
+    "",
+    VARIANT_NUMBER,
+    nullptr,
+    offsetof(nsStylePosition, mAspectRatio),
+    eStyleAnimType_None)
 CSS_PROP_DISPLAY(
     backface-visibility,
     backface_visibility,

layout/style/nsRuleNode.cpp

@@ -8544,6 +8544,12 @@ nsRuleNode::ComputePositionData(void* aStartStruct,
              SETCOORD_UNSET_INITIAL,
            aContext, mPresContext, conditions);
 
+  // aspect-ratio: float, initial
+  SetFactor(*aRuleData->ValueForAspectRatio(),
+           pos->mAspectRatio, conditions,
+           parentPos->mAspectRatio, 0.0f,
+           SETFCT_UNSET_INITIAL | SETFCT_POSITIVE | SETFCT_NONE);
+
   // box-sizing: enum, inherit, initial
   SetValue(*aRuleData->ValueForBoxSizing(),
            pos->mBoxSizing, conditions,

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;

layout/style/nsStyleStruct.h

@@ -1815,6 +1815,7 @@ struct MOZ_NEEDS_MEMMOVABLE_MEMBERS nsStylePosition
   nsStyleCoord  mGridAutoColumnsMax;    // [reset] coord, percent, enum, calc, flex
   nsStyleCoord  mGridAutoRowsMin;       // [reset] coord, percent, enum, calc, flex
   nsStyleCoord  mGridAutoRowsMax;       // [reset] coord, percent, enum, calc, flex
+  float         mAspectRatio;           // [reset] float
   uint8_t       mGridAutoFlow;          // [reset] enumerated. See nsStyleConsts.h
   mozilla::StyleBoxSizing mBoxSizing;   // [reset] see nsStyleConsts.h
 

layout/style/test/ListCSSProperties.cpp

@@ -106,6 +106,7 @@ const char *gInaccessibleProperties[] = {
     "-x-span",
     "-x-system-font",
     "-x-text-zoom",
+    "aspect-ratio",  // for now.
     "-moz-control-character-visibility",
     "-moz-script-level", // parsed by UA sheets only
     "-moz-script-size-multiplier",