[Android] Clear backing SkBitmap before rendering the overscroll effect

content/browser/android/system_ui_resource_manager_impl.cc

Index: content/browser/android/system_ui_resource_manager_impl.cc
diff --git a/content/browser/android/system_ui_resource_manager_impl.cc b/content/browser/android/system_ui_resource_manager_impl.cc
index 80c1c43d5823eb21e9152f3e28f9a576d2ea2b09..81f12fc3a70d5d0abde50158258001d4343c7564 100644
--- a/content/browser/android/system_ui_resource_manager_impl.cc
+++ b/content/browser/android/system_ui_resource_manager_impl.cc
@@ -45,6 +45,7 @@ SkBitmap CreateOverscrollGlowLBitmap(const gfx::Size& screen_size) {
     LOG(FATAL) << " Failed to allocate bitmap of size " << bounds.width() << "x"
                << bounds.height();
   }
+  glow_bitmap.eraseColor(SK_ColorTRANSPARENT);
 
   SkCanvas canvas(glow_bitmap);
   canvas.clipRect(SkRect::MakeXYWH(0, 0, bounds.width(), bounds.height()));