We need to expose a bunch of stuff of UndoStack for idle time spell checker.

Getting rid of the purely virtual interface helps it.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e8238843edf7f903b0ab03ae98a3280138421111

commit e8238843edf7f903b0ab03ae98a3280138421111
Author: xiaochengh <xiaochengh@chromium.org>
Date: Wed Jan 18 08:35:31 2017

Move class EditCommandComposition to UndoStep.h/cpp

This patch moves class |EditCommandComposition| to UndoStep.h/cpp as a
preparation for getting rid of the |UndoStep| interface and using
|EditCommandComposition| directly.

BUG= 682129 
TEST=n/a; no behavior change

Review-Url: https://codereview.chromium.org/2639913002
Cr-Commit-Position: refs/heads/master@{#444304}

[modify] https://crrev.com/e8238843edf7f903b0ab03ae98a3280138421111/third_party/WebKit/Source/core/editing/BUILD.gn
[modify] https://crrev.com/e8238843edf7f903b0ab03ae98a3280138421111/third_party/WebKit/Source/core/editing/commands/CompositeEditCommand.cpp
[modify] https://crrev.com/e8238843edf7f903b0ab03ae98a3280138421111/third_party/WebKit/Source/core/editing/commands/CompositeEditCommand.h
[add] https://crrev.com/e8238843edf7f903b0ab03ae98a3280138421111/third_party/WebKit/Source/core/editing/commands/UndoStep.cpp
[modify] https://crrev.com/e8238843edf7f903b0ab03ae98a3280138421111/third_party/WebKit/Source/core/editing/commands/UndoStep.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/1d898450465e5348f291e38efc2e80684b5134b5

commit 1d898450465e5348f291e38efc2e80684b5134b5
Author: xiaochengh <xiaochengh@chromium.org>
Date: Wed Jan 18 09:37:59 2017

Remove pure-virtual interface UndoStep

This patch removes the pure-virtual interface |UndoStep|, and let its
only implementation |EditCommandComposition| take its place.

Follow up patches will clean up names of classes and functions.

BUG= 682129 

Review-Url: https://codereview.chromium.org/2642653002
Cr-Commit-Position: refs/heads/master@{#444315}

[modify] https://crrev.com/1d898450465e5348f291e38efc2e80684b5134b5/third_party/WebKit/Source/core/editing/commands/UndoStack.cpp
[modify] https://crrev.com/1d898450465e5348f291e38efc2e80684b5134b5/third_party/WebKit/Source/core/editing/commands/UndoStack.h
[modify] https://crrev.com/1d898450465e5348f291e38efc2e80684b5134b5/third_party/WebKit/Source/core/editing/commands/UndoStep.cpp
[modify] https://crrev.com/1d898450465e5348f291e38efc2e80684b5134b5/third_party/WebKit/Source/core/editing/commands/UndoStep.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5e5d50d1fe1c2322b6b2dc07681fd5804de80346

commit 5e5d50d1fe1c2322b6b2dc07681fd5804de80346
Author: xiaochengh <xiaochengh@chromium.org>
Date: Wed Jan 18 09:45:03 2017

Rename class EditCommandComposition to UndoStep

This patch renames class EditCommandComposition to UndoStep to better
match is usage. Follow up patches will clean up remaining names.

BUG= 682129 
TEST=n/a; no behavior change

Review-Url: https://codereview.chromium.org/2642663002
Cr-Commit-Position: refs/heads/master@{#444317}

[modify] https://crrev.com/5e5d50d1fe1c2322b6b2dc07681fd5804de80346/third_party/WebKit/Source/core/editing/Editor.cpp
[modify] https://crrev.com/5e5d50d1fe1c2322b6b2dc07681fd5804de80346/third_party/WebKit/Source/core/editing/Editor.h
[modify] https://crrev.com/5e5d50d1fe1c2322b6b2dc07681fd5804de80346/third_party/WebKit/Source/core/editing/commands/CompositeEditCommand.cpp
[modify] https://crrev.com/5e5d50d1fe1c2322b6b2dc07681fd5804de80346/third_party/WebKit/Source/core/editing/commands/CompositeEditCommand.h
[modify] https://crrev.com/5e5d50d1fe1c2322b6b2dc07681fd5804de80346/third_party/WebKit/Source/core/editing/commands/EditCommand.cpp
[modify] https://crrev.com/5e5d50d1fe1c2322b6b2dc07681fd5804de80346/third_party/WebKit/Source/core/editing/commands/UndoStack.cpp
[modify] https://crrev.com/5e5d50d1fe1c2322b6b2dc07681fd5804de80346/third_party/WebKit/Source/core/editing/commands/UndoStack.h
[modify] https://crrev.com/5e5d50d1fe1c2322b6b2dc07681fd5804de80346/third_party/WebKit/Source/core/editing/commands/UndoStep.cpp
[modify] https://crrev.com/5e5d50d1fe1c2322b6b2dc07681fd5804de80346/third_party/WebKit/Source/core/editing/commands/UndoStep.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/67d2af50c728c4eac309191eaa2d6b4df2f7f718

commit 67d2af50c728c4eac309191eaa2d6b4df2f7f718
Author: xiaochengh <xiaochengh@chromium.org>
Date: Wed Jan 18 10:05:28 2017

Clean up names related to EditCommandComposition

After renaming class |EditCommandComposition| to |UndoStep|, this patch
cleans up the related names:

CompositeEditCommand::composition() -> ::undoStep()
CompositeEditCommand::ensureComposition() -> ::ensureUndoStep()
CompositeEditCommand::appendCommandToComposite() -> :: appendCommandToUndoStep()
CompositeEditCommand::m_composition -> ::m_undoStep

And some other changes to local variable/function names.

BUG= 682129 

Review-Url: https://codereview.chromium.org/2636403002
Cr-Commit-Position: refs/heads/master@{#444322}

[modify] https://crrev.com/67d2af50c728c4eac309191eaa2d6b4df2f7f718/third_party/WebKit/Source/core/editing/Editor.cpp
[modify] https://crrev.com/67d2af50c728c4eac309191eaa2d6b4df2f7f718/third_party/WebKit/Source/core/editing/commands/CompositeEditCommand.cpp
[modify] https://crrev.com/67d2af50c728c4eac309191eaa2d6b4df2f7f718/third_party/WebKit/Source/core/editing/commands/CompositeEditCommand.h
[modify] https://crrev.com/67d2af50c728c4eac309191eaa2d6b4df2f7f718/third_party/WebKit/Source/core/editing/commands/EditCommand.cpp
[modify] https://crrev.com/67d2af50c728c4eac309191eaa2d6b4df2f7f718/third_party/WebKit/Source/core/editing/commands/UndoStep.cpp