[DevTools] Scale context menu position by pageZoomFactor.

BUG=394669

Review URL: https://codereview.chromium.org/396213010

git-svn-id: svn://svn.chromium.org/blink/trunk@178478 bbb929c8-8fbe-4397-9dbb-9b2b20218538
flex shorthand incorrectly accepting 1 0% 1 (i.e. flex-basis in the middle)

On flex items, specifying a flex shorthand with a flex basis in the
middle of two flex factors, e.g. flex: 1 0% 1 is getting accepted in
blink.

According to http://www.w3.org/TR/css3-flexbox/#flex-property, the
grammar of the flex shorthand is as follows:

Value:	none | [ <‘flex-grow’> <‘flex-shrink’>? || <‘flex-basis’> ]

It means that flex-grow and flex-shrink must appear together. Therefore flex
basis in the middle of two flex factors is invalid.

Currently blink consider flex: 1 0% 1 as valid, mapping the values as
 <flex-grow> <flex-basis> <flex-shrink>, i.e. flex: 1 0% 1 is equivalent
to flex: 1 1 0%.

This patch fixes this bug by adding an additional condition checking
if flex-basis is in the middle or not in flex argument list
while setting values for flex basis.

BUG=380984

Review URL: https://codereview.chromium.org/396263003

git-svn-id: svn://svn.chromium.org/blink/trunk@178479 bbb929c8-8fbe-4397-9dbb-9b2b20218538