Move viewport unit resolution to style recalc time

This patch moves the resolution of viewport units to style recalc time.
Currently viewport units are left unresolved during style recalcs which
leads to several problems (see linked bugs). Moving the resolution will
fix these problems, as well as reduce the plumbing that goes on. 

This patch is touches a lot of files since the valueForLength functions
now no longer need a RenderView, but the interesting changes are in:

- CSSToLengthConversionData -> CSSPrimitiveValue, for moving resolution
to style recalc time
- Length / LengthFunction, no longer needs to know about viewport units
- FrameView -> Document -> MatchedPropertiesCache, for scheduling style
recalcs upon resize

Viewport Lengths are currently also used in viewport descriptions (that
is, @viewport and the viewport meta tag). I've added to Length two more
enum values (DeviceWidth and DeviceHeight), alongside ExtendToZoom.

Note that getComputedStyle will now do the right thing and return pixel
values when viewport units are used. This behaviour matches Firefox and
the css3-cascade spec.

I've added a test for the most starred bug (124331) and for the various
other issues fixed by this patch I'll make test-only patches.

Note that calc integration with viewport units will be fixed separately
to simplify reviews.

TBR=dglazkov@chromium.org
BUG=124331,137617,125709,261298,173407,322365,310874,311465

Review URL: https://codereview.chromium.org/82083002

git-svn-id: svn://svn.chromium.org/blink/trunk@164448 bbb929c8-8fbe-4397-9dbb-9b2b20218538