Add an LSAN suppression for gin/object_template_builder.h.

BUG=416665

Review URL: https://codereview.chromium.org/603243005

Cr-Commit-Position: refs/heads/master@{#297350}

tools/lsan/suppressions.txt

@@ -56,6 +56,7 @@ leak:blink::WindowProxy::initializeIfNeeded
 leak:blink::*::*GetterCallback
 leak:blink::CSSComputedStyleDeclaration::create
 leak:blink::V8PerIsolateData::ensureDomInJSContext
+leak:gin/object_template_builder.h
 
 # http://crbug.com/356785
 leak:content::RenderViewImplTest_DecideNavigationPolicyForWebUI_Test::TestBody