Fix another segfault in FlingSchedulerAndroid

host_->GetView() might be null.

Bug: 852264
Change-Id: I18af8aecdff6574a00283bae590aa6edacfbef94
Reviewed-on: https://chromium-review.googlesource.com/1100968Reviewed-by: Sahel Sharifymoghaddam <sahel@chromium.org>
Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567798}

content/browser/renderer_host/input/fling_scheduler_android.cc

@@ -62,6 +62,8 @@ void FlingSchedulerAndroid::ProgressFlingOnBeginFrameIfneeded(
 }
 
 ui::WindowAndroid* FlingSchedulerAndroid::GetRootWindow() {
+  if (!host_->GetView())
+    return nullptr;
   return host_->GetView()->GetNativeView()->GetWindowAndroid();
 }