Use lock-free lazy initialization for static histogram references

tools/valgrind/memcheck/suppressions.txt

 # There are three 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 # running overnight and removing outdated bugs/suppressions.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 859 matching lines @@
    ...
    fun:_ZN4base13OpenTestNSSDBERK8FilePathPKc
 }
 {
    bug_61585c
    Memcheck:Leak
    fun:malloc
    fun:PL_ArenaAllocate
    fun:PORT_ArenaAlloc_Util
 }
+{
+   # Histograms are used on un-joined threads, and can't be deleted atexit.
+   Histograms via FactoryGet including Linear Custom Boolean and Basic
+   Memcheck:Leak
+   fun:_Znw*
+   fun:_ZN4base*Histogram10FactoryGet*
+}
+{
+   # Histograms are used on un-joined threads, and can't be deleted atexit.
+   Histograms via FactoryGet including Stats for disk_cache
+   Memcheck:Leak
+   fun:_Znw*
+   fun:_ZN10disk_cache14StatsHistogram24StatsHistogramFactoryGet*
+}
 
 #-----------------------------------------------------------------------
 # 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).
 
 {
    # Chromium flakily leaks tasks at shutdown, see
    # http://crbug.com/6532
    # http://codereview.chromium.org/20067
    # http://codereview.chromium.org/42083
@@ skipping 3358 matching lines @@
 }
 {
    bug_todo_getdelim
    Memcheck:Leak
    fun:malloc
    fun:getdelim
    ...
    fun:call_init
    fun:_dl_init
 }