Fix crash in WasTargetForLastMouseEvent

The frame could be null, ensure if it is we return early.

BUG=1130991

(cherry picked from commit 789a7a446a2e5ab21edb85e51632cf562a1d0035)

Change-Id: I8ced1223f4beb281adcb06c99d9b0fc4b761333e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2468237
Reviewed-by: Mustaq Ahmed <[email protected]>
Commit-Queue: Dave Tapuska <[email protected]>
Cr-Original-Commit-Position: refs/heads/master@{#816763}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2484952
Reviewed-by: Dave Tapuska <[email protected]>
Cr-Commit-Position: refs/branch-heads/4280@{#486}
Cr-Branched-From: ea420fb963f9658c9969b6513c56b8f47efa1a2a-refs/heads/master@{#812852}
diff --git a/third_party/blink/renderer/core/exported/web_plugin_container_impl.cc b/third_party/blink/renderer/core/exported/web_plugin_container_impl.cc
index 014b5fc..72208a1d 100644
--- a/third_party/blink/renderer/core/exported/web_plugin_container_impl.cc
+++ b/third_party/blink/renderer/core/exported/web_plugin_container_impl.cc
@@ -682,10 +682,10 @@
 }
 
 bool WebPluginContainerImpl::WasTargetForLastMouseEvent() {
-  return element_->GetDocument()
-             .GetFrame()
-             ->GetEventHandler()
-             .GetElementUnderMouse() == element_;
+  auto* frame = element_->GetDocument().GetFrame();
+  if (!frame)
+    return false;
+  return frame->GetEventHandler().GetElementUnderMouse() == element_;
 }
 
 void WebPluginContainerImpl::DidReceiveResponse(