Also, stop pushing the SDK to sky_sdk now that this repo exists.

Track overflow during flex layout and fix stocks row

R=hixie

Fix build issues related to symlink.py

There are actually two uses cases for symlink.py. This CL restores
//build/symlink.py to match the version in Chromium and adds a new version in
////sky/build/symlink.py that works properly for the material-design-icons.

Fix #57 Flex needs to understand baselines

The idea is that AnimatedContainer is a drop-in replacement for Container that
provides implicit animations when its properties change.

R=mpcomplete@google.com

Navigator improvements, avoid building invisible routes

R=abarth

Also fixed roll_versions to no longer roll mojo paths
since those are not part of the sky_engine repository.

R=abarth@google.com

The primary goal of this change was to remove EventTarget from the
sky_engine C++ code. Since EventTarget is so core to the entire event
system that sky_engine was based on, this is a rather invasive change.
As such, it had some knock-on effects. I deleted some of the files
that were affected, and cauterised the remainder.

In many cases, a file would depend on another file that it didn't
include directly, but instead included indirectly via another file
that I deleted. When this happened, if the features that this broke
were obsolete, I sometimes just removed the features instead.

Specifically:
- removed EventTarget
- removed EventQueue, since without a target, what's a queue going to
  do?
- same with EventDispatch*
- removed ExecutionContext, since it had an EventQueue and nothing
  else it did was relevant to Sky anymore
- removed ActiveDOMObject, which was all about ExecutionContexts
- removed ContextLifecycleNotifier since it dependend on
  ExecutionContext and ActiveDOMObject
- removed the other Lifecycle classes for consistency, and replaced
  them with four booleans in the Document class
- removed some of the attributes that are no longer relevant from
  IDLExtendedAttributes (ConstructorCallWith and
  CallWith=ExecutionContext)
- removed the Document member on DOMDartState since we never set it to
  anything but null.
- removed BuiltinSky::InstallWindow since it relied on the Document
  member of DOMDartState
- removed EventHandler, EventListener, and mentions of those in
  various binding scripts
- removed NewEventHandler, since we're not using that either
- removed the following interfaces from the Sky Dart API:
  - EventTarget
  - EventListener (since without a target, there's no way to listen)
  - FocusEvent (since it's only member was an EventTarget)
  - HashChangeEvent (mostly by accident, but it's defunct anyway)
  - FontFace (it used ConstructorCallWith=ExecutionContext)
- changed the following interfaces of the Sky DART API:
  - MediaQueryList is no longer an EventTarget
  - Node is no longer an EventTarget
  - Document no longer has defaultView (depended on
    DOMDartState's document)
  - DocumentFragment, Element, Range, and Text no longer have a
    constructor (they all depended on DOMDartState's document, which
    is now gone)
  - Event lost its EventTarget members and path.
  - Window lost its WindowTimers partial interface (it used
    EventTarget and ExecutionContext a lot)
- removed numerous hacks in the bindings around features that are now
  gone, like addEventListener
- removed a bunch of console logging code, since that relied on
  ExecutionContext
- cauterised the wound in FontFace.cpp by removing constructors and
  methods that called now-removed features
- same with MediaQuery and friends
- same with some editor features and focus-related features
- same with Document
- removed DOMTimer classes since they use ExecutionContexts

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1218593002.

Also added a smoke test for examples/widgets/tabs.dart.

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1213873002.

TBR=abarth

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

Let's hide double.INFINITY a bit more, by providing cleaner APIs for the cases where we're currently trying to use it.

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1209233002.

New asserts:
- verify that after layout, the size fits the constraints
- verify that after layout, the size isn't infinite
- verify that you don't set the size in performLayout() if you have
  sizedByParent set
- verify that nobody reads your size during layout except you, or your
  parent if they said parentUsesSize:true

Fixes some bugs found by those asserts:
- RenderBlock, RenderStack, and RenderScaffold were not always setting
  parentUsesSize correctly
- RenderScaffold was setting its slot entries to null rather than
  removing them when the slot went away, which led to null derefs in
  certain circumstances

Also, rename a local variable in RenderStack.performLayout() because
it was shadowing a variable on the object itself, which was really
confusing when I first tried to debug this function...

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1213473003.

There's is no support for animating the selected tab indicator, there isn't a TabNavigator container yet, overflow layout (tabs don't fit) isn't supported yet, etc.

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

Review URL: https://codereview.chromium.org/1205953002.

Adds documentation to Texture and SpriteSheet

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1212073002.