This reverts commit 4b69cf2c.

Fuchsia is the main consumer of these CIPD packages and - to simplify
its infrastructure - it is migrating its SDK partners over to producing
a CIPD package containing a flat .build-id directory.

This change also updates the CIPD package so that the .build-id
directory is placed at the root.

Bug: fxbug.dev/41443

This makes two changes:
- Adds a way to register a callback for when a FlutterDesktopPluginRegistrarRef is destroyed, and implements the logic to call it in the Windows and Linux embeddings.
- Adds a class to the C++ wrapper that handles making a singleton owning PluginRegistrar wrappers, and destroying them when the underlying reference goes away, to avoid needing that boilerplate code in every plugin's source.

Fixes https://github.com/flutter/flutter/issues/53496

This patch optimizes C++11 range-based for loops where the variable is
copied in each iteration but it would suffice to obtain it by const
reference. This is only applied to loop variables of types that are
expensive to copy which means they are not trivially copyable or have a
non-trivial copy constructor or destructor.

To ensure that it is safe to replace the copy with a const reference
only the following cases are modified:
  * The loop variable is const-qualified.
  * The loop variable is not const, but only const methods or operators
    are invoked on it, or it is used as const reference or value argument
    in constructors or function calls.

This is an application of the internal performance-for-range-copy
clang-tidy analysis.

Breaks CIPD package creation on Fuchsia.

Example error message:

    Directory: /b/s/w/ir/k/recipe_cleanup/tmp9x3dHw is not empty, deleting it.
    Traceback (most recent call last):
      File "/b/s/w/ir/cache/builder/src/flutter/tools/fuchsia/merge_and_upload_debug_symbols.py", line 140, in <module>
        sys.exit(main())
      File "/b/s/w/ir/cache/builder/src/flutter/tools/fuchsia/merge_and_upload_debug_symbols.py", line 131, in main
        HardlinkContents(symbol_dir, out_dir)
      File "/b/s/w/ir/cache/builder/src/flutter/tools/fuchsia/merge_and_upload_debug_symbols.py", line 83, in HardlinkContents
        os.makedirs(dest_dir)
      File "/b/s/w/ir/cache/vpython/9f7888/lib/python2.7/os.py", line 157, in makedirs
        mkdir(name, mode)
    OSError: [Errno 17] File exists: '/b/s/w/ir/k/recipe_cleanup/tmp9x3dHw/.'

This reverts commit 03d5e500.

This reverts commit 03d5e500.

https://dart.googlesource.com/sdk.git/+log/fae35fca47c9..e736495eb7f0

git log fae35fca47c9..e736495eb7f0 --date=short --first-parent --format='%ad %ae %s'
2020-04-03 rnystrom@google.com Migrate language_2/const to NNBD.
2020-04-03 srujzs@google.com [dart:html] Copy and rename lib_2/html to NNBD.
2020-04-02 jwren@google.com Bug fix in inherited_reference_contributor.dart, completions inside of ConstructorDeclarations should include inherited members.
2020-04-02 scheglov@google.com Infer when nullable type parameter type.
2020-04-02 rnystrom@google.com Add a "fork" command to the migration tool.
2020-04-02 alexmarkov@google.com [tests/nnbd] Fix lib/convert/chunked_conversion_utf88_test for strong mode
2020-04-02 srujzs@google.com [dart:html] Add insertAll to ChildrenElementList
2020-04-02 liama@google.com [nnbd/tests] Fix more HTTP/socket strong mode tests
2020-04-02 srujzs@google.com [dart:html] Remove nullability from CssClassSet funcs
2020-04-02 srujzs@google.com [dart:html] Fix nullability for vars with null checks
2020-04-02 scheglov@google.com More work on ConstraintMatchingTest.
2020-04-02 rnystrom@google.com Migrate language_2/covariant_override to NNBD.
2020-04-02 alexmarkov@google.com Update pkg/vm patterns so pkg/vm_service doesn't match them
2020-04-02 brianwilkerson@google.com Clean up OpTypeTest
2020-04-02 sigmund@google.com [tests] adjust error_stack_trace2_test to work also for DDC.
2020-04-02 sstrickl@google.com [vm] Drop WSRs with reachable references, not just allocated.
2020-04-02 rnystrom@google.com Migrate language_2/closure to NNBD.
2020-04-02 liama@google.com [nnbd/lib] Fix some more strong mode tests
2020-04-02 regis@google.com [VM/nnbd] Minor cleanup when checking required named parameter in strong mode.
2020-04-02 alexmarkov@google.com [vm/nnbd] Infer more accurate types for late static fields
2020-04-02 brianwilkerson@google.com Remove an unnecessary type annotation to satisfy a lint
2020-04-02 brianwilkerson@google.com Report more development time metrics
2020-04-02 scheglov@google.com Remove typeParameterType() and replace with typeParameterTypeStar() mostly.
2020-04-02 brianwilkerson@google.com Pull the latest version of pedantic into the SDK
2020-04-02 scheglov@google.com Remove unused TypeComparison.
2020-04-02 scheglov@google.com Replace interfaceType() with interfaceTypeNone() in ConstraintMatchingTest.

Created with:
  gclient setdep -r src/third_party/dart@e736495eb7f0

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/dart-sdk-flutter-engine
Please CC dart-vm-team@google.com on the revert to ensure that a human
is aware of the problem.

To report a problem with the AutoRoller itself, please file a bug:
https://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

Bug: None
Tbr: dart-vm-team@google.com

Fuchsia is the main consumer of these CIPD packages and - to simplify
its infrastructure - it is migrating its SDK partners over to producing
a CIPD package containing a flat .build-id directory.

This change also updates the CIPD package so that the .build-id
directory is placed at the root.

Bug: fxbug.dev/41443