Implement 'will-change' parsing

LayoutTests/compositing/will-change/parse-will-change-expected.txt

Index: LayoutTests/compositing/will-change/parse-will-change-expected.txt
diff --git a/LayoutTests/compositing/will-change/parse-will-change-expected.txt b/LayoutTests/compositing/will-change/parse-will-change-expected.txt
new file mode 100644
index 0000000000000000000000000000000000000000..cb2f0b61dfbbaded6bfc601bafdabfcbc6f83928
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+++ b/LayoutTests/compositing/will-change/parse-will-change-expected.txt
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+Test that setting and getting will-change works as expected
+
+On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
+
+
+Test getting will-change set through CSS
+PASS getComputedStyle(willChangeOpacity, '').getPropertyValue('will-change') is 'opacity'
+PASS getComputedStyle(willChangeScrollPosition, '').getPropertyValue('will-change') is 'scroll-position'
+PASS getComputedStyle(willChangeContents, '').getPropertyValue('will-change') is 'contents'
+PASS getComputedStyle(willChangeMultiple, '').getPropertyValue('will-change') is 'contents, opacity, left, -webkit-transform'
+PASS getComputedStyle(willChangeWithArbitraryIdent, '').getPropertyValue('will-change') is 'opacity, top'
+
+Test initial value of will-change
+PASS getComputedStyle(element, '').getPropertyValue('will-change') is 'auto'
+
+Test getting and setting will-change through JS
+PASS getComputedStyle(element, '').getPropertyValue('will-change') is 'opacity'
+PASS getComputedStyle(element, '').getPropertyValue('will-change') is 'scroll-position'
+PASS getComputedStyle(element, '').getPropertyValue('will-change') is 'contents'
+PASS getComputedStyle(element, '').getPropertyValue('will-change') is 'contents, scroll-position, opacity, -webkit-transform'
+PASS getComputedStyle(element, '').getPropertyValue('will-change') is 'opacity, top'
+PASS getComputedStyle(element, '').getPropertyValue('will-change') is 'opacity, top'
+PASS getComputedStyle(element, '').getPropertyValue('will-change') is 'opacity, top'
+PASS getComputedStyle(element, '').getPropertyValue('will-change') is 'auto'
+
+Test that illegal will-change values are disallowed
+PASS getComputedStyle(element, '').getPropertyValue('will-change') is 'auto'
+PASS getComputedStyle(element, '').getPropertyValue('will-change') is 'auto'
+PASS getComputedStyle(element, '').getPropertyValue('will-change') is 'auto'
+PASS getComputedStyle(element, '').getPropertyValue('will-change') is 'auto'
+PASS getComputedStyle(element, '').getPropertyValue('will-change') is 'auto'
+PASS getComputedStyle(element, '').getPropertyValue('will-change') is 'auto'
+PASS getComputedStyle(element, '').getPropertyValue('will-change') is 'auto'
+PASS getComputedStyle(element, '').getPropertyValue('will-change') is 'auto'
+PASS getComputedStyle(element, '').getPropertyValue('will-change') is 'auto'
+
+Test the value 'initial'
+PASS getComputedStyle(element, '').getPropertyValue('will-change') is 'opacity'
+PASS getComputedStyle(element, '').getPropertyValue('will-change') is 'auto'
+
+Test the value 'inherit'
+PASS getComputedStyle(parentElement, '').getPropertyValue('will-change') is 'contents, opacity, top'
+PASS getComputedStyle(element, '').getPropertyValue('will-change') is 'contents, opacity, top'
+
+Test that will-change is not inherited by default
+PASS getComputedStyle(parentElement, '').getPropertyValue('will-change') is 'opacity'
+PASS getComputedStyle(element, '').getPropertyValue('will-change') is 'auto'
+PASS successfullyParsed is true
+
+TEST COMPLETE
+