Refactoring: Frame::editor() should return a reference.

This CL removes some unnecessary NULL checks.
Inspired by http://trac.webkit.org/changeset/150140 by andersca.

BUG=none
TEST=none; no behavior changes.

Review URL: https://chromiumcodereview.appspot.com/23518002

git-svn-id: svn://svn.chromium.org/blink/trunk@156760 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Tidy up threading-related Blink includes.

On a release build, we no longer leak excessive details about system threading
into the include subtree. Debug builds unaffected for now.

Review URL: https://chromiumcodereview.appspot.com/23453006

git-svn-id: svn://svn.chromium.org/blink/trunk@156761 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Add constants and primitive type readonly attributes to Python IDL compiler

This adds constants to the Python IDL compiler.

As there are no files with only constants, to have real test cases I've
also supported primitive type readonly attributes (currently only have
wrapped readonly attributes),
also moving attribute templates into a macro file.

This allows us to move the following 3 files to Python:
* MallocStatistics.idl
* MemoryInfo.idl
* PerformanceNavigation.idl

The Python generates exactly the same code as the Perl.

About 80 IDL files use constants, but usual other elements as well.

BUG=239771

Review URL: https://chromiumcodereview.appspot.com/23068032

git-svn-id: svn://svn.chromium.org/blink/trunk@156763 bbb929c8-8fbe-4397-9dbb-9b2b20218538