Support author ShadowRoot for APPLET, EMBED, and OBJECT elements.

The behavior is similar to INPUT.  That is to say, we don't allow
<shadow> projecting UA-native view, and an element loses native
behavior if an author ShadowRoot is added.

When an author ShadowRoot is appended, we make  HTMLPlugInElement::
useFallbackContent return true to avoid plugin processing, and request
to reattach.
We add UA ShadowRoot to show a warning about inert <shadow> to
developers.

BUG=301217
R=morrita@chromium.org

Review URL: https://codereview.chromium.org/68133007

git-svn-id: svn://svn.chromium.org/blink/trunk@163140 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Use downloadToFile option when XHR downloads a Blob

Leveraging downloadToFile when XHR downloads a Blob. As a result, a Blob
is downloaded in the browser. It eliminates unnecessary memory copies
between the renderer and the browser.

When downloadToFile options is specified, didDownloadData is called
instead of didReceiveData. So not to break the Inspector, we add the
inspector instrumentations to it.

BUG=269055

Review URL: https://codereview.chromium.org/23444058

git-svn-id: svn://svn.chromium.org/blink/trunk@163141 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove 'hostId()' from WebDevToolsAgentImpl.h

Minor cleanup. It's never called anywhere.

BUG=none.

Review URL: https://codereview.chromium.org/99963006

git-svn-id: svn://svn.chromium.org/blink/trunk@163142 bbb929c8-8fbe-4397-9dbb-9b2b20218538
IDL compiler: [ImplementedAs] interfaces

Test-only change, as already supported in code.

BUG=239771
NOTRY=true
TBR=haraken

Review URL: https://codereview.chromium.org/103593002

git-svn-id: svn://svn.chromium.org/blink/trunk@163143 bbb929c8-8fbe-4397-9dbb-9b2b20218538
IDL compiler: sync Python to r163132

Python side to:
Decouple FileSystem and WebSQL callbacks from VoidCallback and it non-refcounted
https://codereview.chromium.org/103083002/

BUG=239771
BUG=323681
NOTRY=true
TBR=haraken

Review URL: https://codereview.chromium.org/103613002

git-svn-id: svn://svn.chromium.org/blink/trunk@163144 bbb929c8-8fbe-4397-9dbb-9b2b20218538