Fix uninitialized var in DirectRenderer

|visible_| was not initialized, leading to test flakes. Initializing
to false.

TBR=danakj@chromium.org
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_precise_blink_rel

Review-Url: https://codereview.chromium.org/2256903002
Cr-Commit-Position: refs/heads/master@{#412706}

cc/output/direct_renderer.h

@@ -194,7 +194,7 @@ class CC_EXPORT DirectRenderer {
   std::unordered_map<RenderPassId, TileDrawQuad, RenderPassIdHash>
       render_pass_bypass_quads_;
 
-  bool visible_;
+  bool visible_ = false;
 
   // For use in coordinate conversion, this stores the output rect, viewport
   // rect (= unflipped version of glViewport rect), the size of target