Make _initRootBundle more robust

Teaches ChildViewConnection to wrap an existing ViewOwner

fix a mac test

Fixes #1921

Rather than catching every exception, we now handle the one specific case where
we legitimately cannot create the root bundle.

Fixes #900

Add dartdoc to VirtualViewport widgets

Remove dependency on material_design_icons

Random fixes to dartdocs, http lib, analyzer

We get the icons from the iconfont now.

Also, remove the package:flutter CHANGELOG.md.  This file is outdated and the
git history is a more accurate change log these days.

This is a variety of trivial fixes that I collected while going through the dartdocs.
This does contain some non-comment changes.

Update engine.version

Add tests for AssetVendor and resolution-dependent image loading

Remove the one use of DrawLooper

We're going to remove DrawLooper from the canvas API soon.

[ios] use xcrun to launch simulator instead of hardcoded path

Container's child is now inset by the Container's border

Remove test dependency from package:flutter

Fixes #2198

[ios] generate flx on first ios launch

fix the zip tool when building for ios

show stdout on xcode failures

Improve documentation for MultiChildLayoutDelegate

Reorder and document members in ScrollableState

Renames Weather demo

fix the stop command tests

The mojo_sdk has cleaned up its dependencies, so we no longer need to depend on
package:test from package:flutter.

Switch from hack_load_vm_file_hook to PlatformPlugin