IDL compiler: avoid include for WindowMediaSource.idl

WindowMediaSource.idl is a partial interface for Window.
Thus normally we should include WindowMediaSource.h.
However, this is only constructor attributes, so there's no implementation
and no header.

Python determines the includes at the dependency resolution stage,
just checking the partial interface and if there's an [ImplementedAs].

Perl instead computes the includes at every member, hence b/c there
are only constructors it doesn't trigger it here.

Now, we don't want to have to parse all member of a partial interface
to determine if we need a header!

Conveniently, we have an existing extended attribute that says
"no header", namely [LegacyImplementedInBaseClass].

There are thus 3 clean solutions to this:
1. Add an empty header, WindowMediaSource.h;
   thus we can always include the header (unless implemented elsewhere).
2. Add a new extended attribute, [NoHeader], used only here.
3. Use the existing [LegacyImplementInBaseClass];
if we get rid of other cases, can rename to [NoHeader].

I think 1. (always include the header) is cleanest, as it minimizes logic.
However, this CL is simplest (it does 3), as it uses existing logic.

WDYT?

R=haraken

Review URL: https://codereview.chromium.org/156573002

git-svn-id: svn://svn.chromium.org/blink/trunk@166672 bbb929c8-8fbe-4397-9dbb-9b2b20218538
[import] Refactoring: Extract HTMLImportState

This is follow up of r165624.
Now HTMLImport::State is encapsulated in HTMLImportState class.

BUG=none
TEST=none

Review URL: https://codereview.chromium.org/137723011

git-svn-id: svn://svn.chromium.org/blink/trunk@166673 bbb929c8-8fbe-4397-9dbb-9b2b20218538
[Font Load Events] Fix crash on FontFaceSet methods when document is destroyed

It is possible that when a method of FontFaceSet is called, its owner
document is already destroyed. We should check existence of document at
each method entry.

BUG=341330
TEST=fast/css/fontfaceset-unattached-document.html

Review URL: https://codereview.chromium.org/132753007

git-svn-id: svn://svn.chromium.org/blink/trunk@166674 bbb929c8-8fbe-4397-9dbb-9b2b20218538