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/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,