Fixed bug in vm/benchmark_test.h

Fixed bug in vm/benchmark_test.h

The Benchmark objects were marked as 'const', but Benchmark::CreateIsolate
writes to 'Benchmark::isolate_'. This was not discovered so far, since GCC
places the global Benchmark objects into a read-write section.

It turns out that clang is able to create the const Benchmark objects at
compile time and puts them into a read-only section of the ELF file (it probably
inlines the constructor).
Thus, at runtime Benchmark::CreateIsolate tries to write to a read-only address
and crashes with a SEGV.

R=iposva@google.com

Committed: https://code.google.com/p/dart/source/detail?r=22415

[Ivan Posva, 2013-05-06 14:44:31]

LGTM -ip

https://codereview.chromium.org/14988005/diff/1/runtime/vm/benchmark_test.h
File runtime/vm/benchmark_test.h (right):

https://codereview.chromium.org/14988005/diff/1/runtime/vm/benchmark_test.h#n...
runtime/vm/benchmark_test.h:90: Dart_Isolate isolate_;
isolate_ is just the first victim, but there are more fields that are not const
in this structure, such as score_.

[kustermann, 2013-05-06 14:49:30]

Committed patchset #1 manually as r22415 (presubmit successful).

[kustermann, 2013-05-06 15:13:37]

On 2013/05/06 14:49:30, kustermann wrote:
> Committed patchset #1 manually as r22415 (presubmit successful).

Thank you.

Now the our clang 'vm-linux-release' builder on FYI is green (see:
http://build.chromium.org/p/client.dart.fyi/builders/vm-linux-release/builds/105).

We'll probably switch to clang on our vm builders on the main waterfall soonish
:-)