Suppresses occasional leaks for Bug 69919

This change suppresses occasional leaks for Bug 69919. (Even though these leak do not happen always, they happen pretty often.)

TBR=thestig,timurrrr
BUG=69919
TEST=make the "Linux Tests (valgrind)(1)" bot green.

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@71633 0039d316-1c4b-4281-b951-d872f2087c98

tools/valgrind/memcheck/suppressions.txt

@@ -3581,3 +3581,12 @@
    ...
    fun:*SpeexEncoderC1Ei
 }
+{
+   Bug_69919
+   Memcheck:Leak
+   fun:calloc
+   ...
+   fun:_ZN3gfx15OSMesaGLContext10InitializeEjPNS_9GLContextE
+   fun:_ZN3gfx9GLContext24CreateOffscreenGLContextEPS0_
+   fun:*InitializeGLContextEv
+}