Have content/ create and destroy its own threads.

tools/valgrind/memcheck/suppressions.txt

 # There are four kinds of suppressions in this file.
 # 1. third party stuff we have no control over
 #
 # 2. intentional unit test errors, or stuff that is somehow a false positive
 # in our own code, or stuff that is so trivial it's not worth fixing
 #
 # 3. Suppressions for real chromium bugs that are not yet fixed.
 # These should all be in chromium's bug tracking system (but a few aren't yet).
 # Periodically we should sweep this file and the bug tracker clean by
 # running overnight and removing outdated bugs/suppressions.
@@ skipping 5154 matching lines @@
    fun:_ZNK7WebCore30SVGTextLayoutAttributesBuilder25propagateLayoutAttributesEPNS_12RenderObjectERN3WTF6VectorINS_23SVGTextLayoutAttributesELm0EEERjRt
 }
 {
    # ProcessSingleton::LinuxWatcher is marked DeleteOnIOThread.  Sometimes it
    # leaks on shutdown instead of getting deleted.  The destructor doesn't do
    # anything important, so this shouldn't be a big deal.
    bug_104578
    Memcheck:Leak
    fun:_Znw*
    fun:_ZN16ProcessSingletonC1ERK8FilePath
-   fun:_ZN22ChromeBrowserMainParts25PreMainMessageLoopRunImplEv
+   fun:_ZN22ChromeBrowserMainParts20PreCreateThreadsImplEv
 }
 {
    bug_104690
    Memcheck:Leak
    fun:malloc
    fun:g_malloc
    fun:g_slice_alloc
    fun:g_slice_alloc0
    fun:g_type_create_instance
    fun:g_object_constructor
@@ skipping 134 matching lines @@
    obj:/lib/libselinux.so.1
    obj:/lib/libselinux.so.1
 }
 {
    bug_todo_grep
    Memcheck:Leak
    fun:malloc
    obj:/bin/grep
    obj:/bin/grep
 }