This CL restores fast incremental builds in ninja when changing IDLs.

At some point incremental builds got broken, and any IDL file change triggered a long recompile process, even:
touch Source/core/dom/Node.idl 

This is because preprocess_idls.py was ignoring --write-file-only-if-changed for the Global Constructor Partial Interface files (generated IDL files) and the Event Names file (EventNames.in). Thus any change to any IDL file updated these files and rebuilt dependent targets.

This CL fixes this by making preprocess_idls.py respect --write-file-only-if-changed for all its output files.

Review URL: https://chromiumcodereview.appspot.com/18747002

git-svn-id: svn://svn.chromium.org/blink/trunk@153622 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Custom Element Registry: Use the original type for definition lookup.

Use the type from instantiation time, not the current 'is' attribute,
when looking up the Element definition.

The spec (https://dvcs.w3.org/hg/webcomponents/raw-file/tip/spec/custom/index.html) says:
"After a custom element is instantiated, changing the value of the is attribute must not affect this element's custom element type."

It was possible to change a instantiated type extension's 'is' attribute before its definition was registered to break the above assertion.

BUG=234509

Review URL: https://chromiumcodereview.appspot.com/18094005

git-svn-id: svn://svn.chromium.org/blink/trunk@153623 bbb929c8-8fbe-4397-9dbb-9b2b20218538