Make SyncCallbackHelper ref counted.

SyncCallbackHelper is unsafely referenced from the success and error callbacks which have lifetime determined by the callback receivers.
This CL allocates SyncCallbackHelper on the heap and uses ref counting to ensure it's alive so long as the callbacks are.

This CL also adds proper tracing of heap-allocated callback arguments when scheduling callbacks for the oilpan build.

BUG=

Review URL: https://codereview.chromium.org/212623011

git-svn-id: svn://svn.chromium.org/blink/trunk@170434 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Move 'IDLExtendedAttributes.txt' filename to idl_validator.py

Currently 'IDLExtendedAttributes.txt' is hard-coded 4 places:
twice in .gyp, once in r-b-t (Tools/Scripts/webkitpy/bindings/main.py),
once in an error message
...and then passed down several levels to idl_validator.py where
it's actually used.
This is brittle (because r-b-t has a distant dependence on a path)
and verbose (we have yet another parameter to the compiler script and
constructors).

This moves the filename to idl_validator, reducing this to 2 places, not 4.
This means:
* r-b-t no longer depends on the file organization in bindings/,
* we can simplify the parameter lists, and
* the error message is up-to-date.

We still have the filename in .gyp (in the 'inputs'), which ensures it's
there and prevents build breakage.

R=haraken
BUG=341748

Review URL: https://codereview.chromium.org/218903002

git-svn-id: svn://svn.chromium.org/blink/trunk@170435 bbb929c8-8fbe-4397-9dbb-9b2b20218538