Canvas2d: Implement rerouting event by hit region's control.

third_party/WebKit/Source/modules/canvas2d/HitRegion.cpp

Index: third_party/WebKit/Source/modules/canvas2d/HitRegion.cpp
diff --git a/third_party/WebKit/Source/modules/canvas2d/HitRegion.cpp b/third_party/WebKit/Source/modules/canvas2d/HitRegion.cpp
index 77acbb53dfc781246bf1e40246fdfe2aeda4f6d9..4423f63ba2b4b30065e9dbb7a6214b60128fa64c 100644
--- a/third_party/WebKit/Source/modules/canvas2d/HitRegion.cpp
+++ b/third_party/WebKit/Source/modules/canvas2d/HitRegion.cpp
@@ -10,7 +10,7 @@
 namespace blink {
 
 HitRegion::HitRegion(const Path& path, const HitRegionOptions& options)
-    : m_id(options.id())
+    : m_id(options.id().isEmpty() ? String() : options.id())
     , m_control(options.control())
     , m_path(path)
 {