Run worker processes via the zygote.

The following tests fail when using the SUID sandbox because they try to count
processes and the extra sandbox processes throw them off. They pass with this
patch so long as the SUID sandbox isn't invoked (which is the case on the
builders):
 WorkerTest.FLAKY_MultipleTabsQueuedSharedWorker
 WorkerTest.FLAKY_LimitPerPage
 WorkerTest.WorkerClose
 WorkerTest.QueuedSharedWorkerShutdown
 WorkerTest.FLAKY_QueuedSharedWorkerStartedFromOtherTab

Note that this patch doesn't trigger the seccomp sandbox for worker
processes.  That will have to wait for another CL.

BUG=54794
TEST=ui_tests

http://codereview.chromium.org/3312021/show

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@59242 0039d316-1c4b-4281-b951-d872f2087c98
void ChromeAssert(const std::string& str) {
  typedef void (__cdecl *DumpProcessFunction)();
  DumpProcessFunction DumpProcess = reinterpret_cast<DumpProcessFunction>(
      ::GetProcAddress(::GetModuleHandle(chrome::kBrowserProcessExecutableName),
                       "DumpProcess"));
  if (DumpProcess)
    DumpProcess();
}

void ChromeAssert(const std::string& str) {
  typedef void (__cdecl *DumpProcessFunction)();
  DumpProcessFunction DumpProcess = reinterpret_cast<DumpProcessFunction>(
      ::GetProcAddress(::GetModuleHandle(chrome::kBrowserProcessExecutableName),
                       "DumpProcess"));
  if (DumpProcess)
    DumpProcess();
}
