Suppress unitialized use of memory for random_number_ seed

I'm going to TBR this, since it causes a bunch of redness
on the tree, and is really a supression.

tbr=rtenneti,mk
bug=106326
Review URL: http://codereview.chromium.org/8792005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@112937 0039d316-1c4b-4281-b951-d872f2087c98

base/tracked_objects.cc

@@ -9,6 +9,7 @@
 #include "base/format_macros.h"
 #include "base/message_loop.h"
 #include "base/stringprintf.h"
+#include "base/third_party/valgrind/memcheck.h"
 #include "base/threading/thread_restrictions.h"
 #include "build/build_config.h"
 #include "base/port.h"
@@ -218,6 +219,8 @@ ThreadData::ThreadData(int thread_number)
 ThreadData::~ThreadData() {}
 
 void ThreadData::PushToHeadOfList() {
+  VALGRIND_MAKE_MEM_DEFINED_IF_ADDRESSABLE(&random_number_,
+                                           sizeof(random_number_));
   // Toss in a hint of randomness (atop the uniniitalized value).
   random_number_ += static_cast<int32>(this - static_cast<ThreadData*>(0));
   random_number_ ^= (Now() - TrackedTime()).InMilliseconds();