Add collection of PlatformViews to the Shell and allow them to be queried over the service protocol (#2861)

* Adopt //lib/tonic/logging

* Adopt //lib/tonic/scopes

* Adopt //lib/tonic/parsers

Also, switch over to //lib/tonic's typed data classes.

Hopefully this will build this time.

* Remove time

* Remove rand

* Remove array buffers

* Remove more code

* Remove more image decoding code

* Remove more code

* Remove old public API

* Remove more old public headers

* Remove layout test support

* Remove WebPrivateOwnPtr

* Remove WebString

* Remove worker pool

We will eventually remove our version of tonic and use this one instead.

This patch removes a bunch of dead code in //skia/ext.

Also, remove the hacks that integrate Skia ref counting with WTF. Now we
just use sk_sp everywhere for managing Skia ref counts.

We don't use this anymore.

Fallback to creating Skia managed images on platforms that dont provide a GL context on the resource loader. (#2849)

This patch introduces a //glue library that isolates our dependency on //base.
This will let us clean up our //base dependencies ahead of actually being able
to fully remove them.

This patch removes almost all //base dependency of //flow. The only dependency
left is on tracing.

This patch starts the process of porting Flutter to run on Fuchsia by
adding FTL to DEPS. We will eventually replace //base with //lib/ftl.

The buildbot and Travis are running inconsistent versions of the analyzer

The LayerTree may be holding references to obsolete Skia/GPU resources,
notably the GrGLGpu.  The old GrGLGpu should be deleted before a new
GrGLGpu is created during the next rasterizer setup.

Fixes https://github.com/flutter/flutter/issues/5074

RRect.fromLTRBCustom -> RRect.fromLTRBAndCorners
RRect.fromRectCustom -> RRect.fromRectAndCorners

trailing space rather than after.

We were including an empty rectangle in the list of TextBoxes for that
range.

BUG=https://github.com/flutter/flutter/issues/4911

* Compile in SIMD related file on SK_CPU_X86. Fixes iOS simulator builds.
* Unconditionally enable SIMD use on arm64.