Code:  void DesktopWindowTreeHostX11::SetVisible(bool visible) {
   if (compositor())
     compositor()->SetVisible(visible);
  if (IsVisible() != visible)
    native_widget_delegate_->OnNativeWidgetVisibilityChanged(visible);
 }

Vulnerability Type: Bypass 
CWE ID: CWE-284
Summary: The extensions API in Google Chrome prior to 55.0.2883.75 for Mac, Windows and Linux, and 55.0.2883.84 for Android incorrectly permitted access to privileged plugins, which allowed a remote attacker to bypass site isolation via a crafted HTML page.
Commit Message: Fix PIP window being blank after minimize/show

DesktopWindowTreeHostX11::SetVisible only made the call into
OnNativeWidgetVisibilityChanged when transitioning from shown
to minimized and not vice versa.  This is because this change
https://chromium-review.googlesource.com/c/chromium/src/+/1437263
considered IsVisible to be true when minimized, which made
IsVisible always true in this case.  This caused layers to be hidden
but never shown again.

This is a reland of:
https://chromium-review.googlesource.com/c/chromium/src/+/1580103

Bug: 949199
Change-Id: I2151cd09e537d8ce8781897f43a3b8e9cec75996
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1584617
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: enne <enne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#654280}