Blink GC plugin: Ensure that classes with virtual trace methods always have vtables for their left-…

Blink GC plugin: Ensure that left-most vtable is the first thing to be initialized for polymorphic classes with trace methods.
    
This is done by ensuring one of two properties for any polymorphic class with a trace method.
1. If the trace method is virtual, then the left-most base class must define a virtual trace method too.
2. If the trace method is non-virtual, then the left-most base class must define some virtual method.

BUG=334149
R=ager@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=289285

[Mads Ager (chromium), 2014-08-11 13:11:01]

LGTM!

[zerny-chromium, 2014-08-11 14:51:13]

Updated exception for GCMixin.

PTAL at the Blink side change needed to pass these checks is at:
https://codereview.chromium.org/463543002

[zerny-chromium, 2014-08-13 12:12:34]

Updated with weaker requirements. Now we don't require trace to be virtual for
polymorphic classes, only that the left-most (non GC) base class is
polymorphic/defines a virtual function.

PTAL. The Blink side change will be updated (simplified) shortly.

[Mads Ager (chromium), 2014-08-13 12:23:58]

LGTM

https://codereview.chromium.org/455263004/diff/40001/tools/clang/blink_gc_plu...
File tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp (right):

https://codereview.chromium.org/455263004/diff/40001/tools/clang/blink_gc_plu...
tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp:921: 
Remove extra empty line?

https://codereview.chromium.org/455263004/diff/40001/tools/clang/blink_gc_plu...
tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp:1002: // Stop with the left-most
prior to a safe polymorphic base, ie, the a
the a -> the

[zerny-chromium, 2014-08-13 12:50:35]

https://codereview.chromium.org/455263004/diff/40001/tools/clang/blink_gc_plu...
File tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp (right):

https://codereview.chromium.org/455263004/diff/40001/tools/clang/blink_gc_plu...
tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp:921: 
On 2014/08/13 12:23:58, Mads Ager (chromium) wrote:
> Remove extra empty line?

Done.

https://codereview.chromium.org/455263004/diff/40001/tools/clang/blink_gc_plu...
tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp:1002: // Stop with the left-most
prior to a safe polymorphic base, ie, the a
On 2014/08/13 12:23:58, Mads Ager (chromium) wrote:
> the a -> the

Also removed the ambiguity of "the base".

[zerny-chromium, 2014-08-13 12:50:38]

The CQ bit was checked by zerny@chromium.org

[commit-bot: I haz the power, 2014-08-13 12:51:08]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/zerny@chromium.org/455263004/60001

[commit-bot: I haz the power, 2014-08-13 14:02:22]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  linux_chromium_gn_rel on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[commit-bot: I haz the power, 2014-08-13 14:13:16]

Committed patchset #4 (60001) as 289285