Refactor sources and derived sources in derived_sources.gyp
Refactor sources and derived sources in derived_sources.gyp

This is a refactoring patch in preparation for adding a Python IDL
compiler in parallel with the Perl IDL compiler, so we can move IDL files
individually from the Perl compiler to the Python compiler.

Currently compiling .idl to .cpp/.h and aggregating the .cpp into
V8DerivedSources*.cpp is done in one step.
This splits it into two, which will let us split up the compiling
into Perl and Python, and then do the aggregation.

Also some minor cleaning:
* removing duplicate dependencies
  (since target supplemental_dependencies is specified,
   don't need to also list individual files);
* regularize command line (put argument last, after flags)
  and add note about invisible dependency by a sed script.

(To be followed by CL splitting the compile step into Perl + Python,
 with stub Python compiler.)

BUG=239771

Review URL: https://chromiumcodereview.appspot.com/18346015

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@153559 bbb929c8-8fbe-4397-9dbb-9b2b20218538

primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs