Suppress an uninitialized value in KeyboardLayoutManager::SetChildBounds.

BUG=407467
TBR=bshe@chromium.org

Review URL: https://codereview.chromium.org/502183003

Cr-Commit-Position: refs/heads/master@{#291851}

tools/valgrind/memcheck/suppressions.txt

@@ -6283,3 +6283,9 @@
    fun:_ZN5blink11RenderBlock13paintContentsERNS_9PaintInfoERKNS_11LayoutPointE
    fun:_ZN5blink11RenderBlock11paintObjectERNS_9PaintInfoERKNS_11LayoutPointE
 }
+{
+   bug_407467
+   Memcheck:Uninitialized
+   fun:_ZN8keyboard21KeyboardLayoutManager14SetChildBounds*
+   fun:_ZN4aura6Window9SetBounds*
+}