Enable asynchrony test.

This test passes now that dartbug.com/21252 has been fixed.

R=danrubel@google.com

Review URL: https://codereview.chromium.org//700723006

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41579 260f80e4-7a28-3924-810f-c04153c831b5
Fix integration test to avoid new 'Unused local variable' hint.

R=scheglov@google.com

Review URL: https://codereview.chromium.org//700323004

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41580 260f80e4-7a28-3924-810f-c04153c831b5
Work around GCC bug that results in incorrect simd128_value_t copying.

Under certain conditions GCC on x86 decides to copy simd128_value_t through FPU stack.

For example Int32x4::value getter would contain the following code:

   212d5: d9 46 07              fld    DWORD PTR [esi+0x7]
   212d8: d9 46 0b              fld    DWORD PTR [esi+0xb]
   212db: 8b 46 03              mov    eax,DWORD PTR [esi+0x3]
   212de: d9 46 0f              fld    DWORD PTR [esi+0xf]
   212e1: d9 ca                 fxch   st(2)
   212e3: d9 5b 04              fstp   DWORD PTR [ebx+0x4]
   212e6: d9 5b 08              fstp   DWORD PTR [ebx+0x8]
   212e9: 89 03                 mov    DWORD PTR [ebx],eax
   212eb: d9 5b 0c              fstp   DWORD PTR [ebx+0xc]

This code is incorrect. For example an attempt to copy an int32_t value that
looks like sNaN will result in it turning into a qNaN which changes
the value being copied.

GCC bug: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58416

This was causing flakiness when people were running WebSocket related tests
locally on Dart VM binaries built with GCC as our WebSocket implementation uses
Int32x4 values to speed up payload masking/unmasking.

Bots were not affected because they are building with clang.

BUG=http://dartbug.com/21220
R=johnmccutchan@google.com

Review URL: https://codereview.chromium.org//692703003

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41581 260f80e4-7a28-3924-810f-c04153c831b5