Created attachment 182263 [details]
If you're transitioning on a length property from a pixel value to a percent and you call getComputedStyle to check the current value we return null because you end up in CSSPrimitiveValue::CSSPrimitiveValue(const Length& length) with the type Calculated which hits an ASSERT_NOT_REACHED();
In a release build we return null because of error handling in CSSComputedStyleDeclaration.
+ccing Mike Lawther, as he's the calc() author.
This appears to actually be related to Bug 29084, top/bottom/left/right all seem to work differently and hence behave as this bug reports. Width works as expected by this test.
This issue is fixed by the patch found in Bug 29084.
On animation from pixels to percent returns null or asserts, When you still doing your work on it in that time you can easily fix it and also can choose everything which create the most of the perfect https://essay-reviewer.com/paperfellows-com-review/ animation. But must care for the pixels which is important for you.