[MemSheriff] Unaddressable Access suppression

BUG=463261
TBR=enne@chromium.org, thestig@chromium.org

Review URL: https://codereview.chromium.org/971953002

Cr-Commit-Position: refs/heads/master@{#318796}

tools/valgrind/drmemory/suppressions.txt

@@ -750,3 +750,12 @@ skia.dll!SkPaint::measure_text
 skia.dll!SkPaint::measureText
 content.dll!content::DoPreSandboxWarmupForTypeface
 content.dll!content::`anonymous namespace'::WarmupDirectWrite
+
+UNADDRESSABLE ACCESS
+name=http://crbug.com/463261
+...
+blink_web.dll!blink::WebFrameWidgetImpl::selectionBounds
+content.dll!content::RenderWidget::GetSelectionBounds
+content.dll!content::RenderWidget::UpdateSelectionBounds
+content.dll!content::RenderWidget::willBeginCompositorFrame
+cc.dll!base::internal::InvokeHelper<>::MakeItSo