Also, fixes the stocks list to work properly including hit testing at
the bottom of the screen.

New classes:

RenderViewport: a class that supports positioning a child inside
itself and offsetting it.

Viewport: a RenderObjectWrapper that wraps RenderViewport.

ScrollableViewport: a Component that hooks Viewport up to some
scrolling behaviour.

Code changes:

RenderBlock now only works when it has an unbounded height constraint.
I removed the clipping in there since it's no longer needed.

I made FixedHeightScrollable use Viewport instead of hand-rolling its
clipping with Transform and Clip. This is what fixes the stocks list
hit testing at the bottom of the screen.

I made anywhere that used to use Block now use ScrollableViewport.

RenderFlex now takes a list of children.

Justifications for test changes:

tests/examples/stocks: changing FixedHeightScrollable to use a
RenderViewport instead of a RenderClipRect/RenderTransform combination
removes the use of an actual transform.

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1223153004 .

R=jackson@google.com

Review URL: https://codereview.chromium.org/1229353002 .

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1231203002 .

R=chinmaygarde@google.com

Review URL: https://codereview.chromium.org/1232063004 .

This entails:
 - Making the baseline logic cache results.
 - Making the baseline logic track who used its information.
 - Making the baseline logic mark all ancestors up to whoever used
   its information wheneven its node gets markNeedsLayout.
 - Making RenderShrinkWrapWidth make its child respect the step width
   and step height, rather than just sizing the child then snapping.
   This is required to make the ink splashes render right on menus
   that are snapped.
 - Adding debugDescribeSettings() to RenderShrinkWrapWidth.
 - Introducing a RenderBaseline class that offsets its child to a
   certain baseline.
 - Factoring out some common code from RenderBaseline and
   RenderPositionedBox to RenderShiftedBox.
 - Redoing all the menu layout logic.

BUG=
R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1219113003.

Rename RenderCanvas to PaintingCanvas to avoid confusion with other classes that inherit from RenderObject.

R=ianh@google.com, abarth@google.com

Review URL: https://codereview.chromium.org/1217933002.

This should be a perf win, but I haven't tested it.

Also adds an operator overloading such that Offset + Size -> Rect.
Also adds Rect.fromLTWH().

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1209413004.

TBR=abarth

Review URL: https://codereview.chromium.org/1208293002.

This also fixes the C++ side to give the right baseline information.
Previously it was giving the baseline distance for the font, but not
for the actual laid-out text.

I considered also providing a "defaultBaseline" accessor that returns
the distance for the actual dominant baseline, but it turns out right
now we never decide the baseline is ideographic. We always use the
alphabetic baseline. We should probably fix that...

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/1200233002.

Decouple Canvas from DisplayList and map Picture and PictureRecorder more directly to their Skia counterparts.

Also changes the framework dart code to use the
refactored APIs and fixes the various examples and
tests.

R=abarth@chromium.org, ianh@chromium.org

Review URL: https://codereview.chromium.org/1190123003.

This CL moves the bulk of the SkyView code out of the |framework| directory
because the |framework| directory was redundant in Dart package import
declarations.

TBR=ianh@google.com

Review URL: https://codereview.chromium.org/1177383006.

R=abarth@chromium.org, abarth, hansmuller

Review URL: https://codereview.chromium.org/1181533003

R=abarth@chromium.org, hixie

Review URL: https://codereview.chromium.org/1181523002

R=abarth@chromium.org, abarth

Review URL: https://codereview.chromium.org/1176053002

Renders interactive_flex and stocks demos fine. Could use more testing,
so I'm going to work on that after I land this.

R=abarth@chromium.org, abarth

Review URL: https://codereview.chromium.org/1173493003

This CL pulled an implementation of position: absolute in RenderStackContainer.

R=eseidel@chromium.org, ianh@google.com

Review URL: https://codereview.chromium.org/1166363002.

This CL splits getIntrinsicDimensions into getMinIntrinsicWidth,
getMaxIntrinsicWidth, getMinIntrinsicHeight, and getMaxIntrinsicHeight so that
we can properly shrink-wrap the stocks app menu. This CL just contains the
refactoring. The use in stocks app will come in a later CL.

R=ianh@google.com

Review URL: https://codereview.chromium.org/1167293003

R=abarth@chromium.org, abarth

Review URL: https://codereview.chromium.org/1164363002

Export Point, Size, Rect, Color, Paint, Path, BoxDecoration, Border, BorderSide, EdgeDims, and FlexDirection from fn2.dart
That way most of our libraries don't have to use sky.Foo all over the place, and we can reduce the number of imports in most Dart components.

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1161323004

This makes debugging the render tree a lot easier. Just print the node
you care about, and you get an indented tree view of its subtree,
including settings. New subclasses should implement the new virtual
method debugDescribeSettings() to expose new settings.

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/1157993005

https://www.dartlang.org/articles/style-guide/#names

R=jackson@google.com

Review URL: https://codereview.chromium.org/1158813004

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1165013003

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/1166773003

TBR=ianh@google.com

Review URL: https://codereview.chromium.org/1154013006

Previously layout2.dart was a thousand lines long.

R=ianh@google.com

Review URL: https://codereview.chromium.org/1161003002