Have Chrome draw top window border when using custom titlebar.

chrome/browser/ui/views/frame/browser_desktop_window_tree_host_win.cc

Index: chrome/browser/ui/views/frame/browser_desktop_window_tree_host_win.cc
diff --git a/chrome/browser/ui/views/frame/browser_desktop_window_tree_host_win.cc b/chrome/browser/ui/views/frame/browser_desktop_window_tree_host_win.cc
index 406f558591156c6dcc7fb37d47dec0a7aa77d122..ba1ecb84674a4e16f176119cbf9aa3d1a1c27359 100644
--- a/chrome/browser/ui/views/frame/browser_desktop_window_tree_host_win.cc
+++ b/chrome/browser/ui/views/frame/browser_desktop_window_tree_host_win.cc
@@ -101,7 +101,8 @@ bool BrowserDesktopWindowTreeHostWin::GetClientAreaInsets(
         display::win::ScreenWin::GetSystemMetricsForHwnd(
             GetHWND(), SM_CXSIZEFRAME);
     // Reduce the Windows non-client border size because we extend the border
-    // into our client area in UpdateDWMFrame().
+    // into our client area in UpdateDWMFrame(). The top inset must be 0 or
+    // else Windows will draw a full native titlebar outside the client area.
     *insets = gfx::Insets(0, frame_thickness, frame_thickness,
                           frame_thickness) - GetClientEdgeThicknesses();
   }
@@ -173,10 +174,10 @@ void BrowserDesktopWindowTreeHostWin::PostHandleMSG(UINT message,
       // unless necessary to avoid flicker. This may be invoked during creation
       // on XP and before the non_client_view has been created.
       WINDOWPOS* window_pos = reinterpret_cast<WINDOWPOS*>(l_param);
-      if (window_pos->flags & SWP_SHOWWINDOW &&
-          GetWidget()->non_client_view()) {
-        GetWidget()->non_client_view()->Layout();
-        GetWidget()->non_client_view()->SchedulePaint();
+      views::NonClientView* non_client_view = GetWidget()->non_client_view();
+      if (window_pos->flags & SWP_SHOWWINDOW && non_client_view) {
+        non_client_view->Layout();
+        non_client_view->SchedulePaint();
       }
       break;
     }
@@ -199,6 +200,13 @@ void BrowserDesktopWindowTreeHostWin::PostHandleMSG(UINT message,
       }
       break;
     }
+    case WM_DWMCOLORIZATIONCOLORCHANGED: {
+      // The activation border may have changed color.
+      views::NonClientView* non_client_view = GetWidget()->non_client_view();
+      if (non_client_view)
+        non_client_view->SchedulePaint();
+      break;
+    }
   }
 }
 
@@ -250,20 +258,6 @@ void BrowserDesktopWindowTreeHostWin::FrameTypeChanged() {
 // BrowserDesktopWindowTreeHostWin, private:
 
 void BrowserDesktopWindowTreeHostWin::UpdateDWMFrame() {
-  // With a custom titlebar we want the margins to always be 2 pixels, because
-  // that gives us the 1 pixel accent color border around the window (a 1 pixel
-  // margin is not sufficient, it will draw a messed-up-looking border instead).
-  // The other pixel ends up being 1-pixel-thick native titlebar (including
-  // caption buttons) but since we draw over that pixel in
-  // GlassBrowserFrameView::PaintTitlebar() it will be invisible and won't get
-  // mouse events.
-  if (browser_frame_->CustomDrawSystemTitlebar() && ShouldUseNativeFrame() &&
-      !GetWidget()->IsFullscreen()) {
-    MARGINS margins = {2, 2, 2, 2};
-    DwmExtendFrameIntoClientArea(GetHWND(), &margins);
-    return;
-  }
-
   // For "normal" windows on Aero, we always need to reset the glass area
   // correctly, even if we're not currently showing the native frame (e.g.
   // because a theme is showing), so we explicitly check for that case rather
@@ -299,9 +293,9 @@ BrowserDesktopWindowTreeHostWin::GetClientEdgeThicknesses() const {
 }
 
 MARGINS BrowserDesktopWindowTreeHostWin::GetDWMFrameMargins() const {
-  // If we're using the opaque frame or we're fullscreen we don't extend the
-  // glass in at all because it won't be visible.
-  if (!ShouldUseNativeFrame() || GetWidget()->IsFullscreen())
+  // Don't extend the glass in at all if it won't be visible.
+  if (!ShouldUseNativeFrame() || GetWidget()->IsFullscreen() ||
+      browser_frame_->CustomDrawSystemTitlebar())
     return MARGINS{0};
 
   // The glass should extend to the bottom of the tabstrip.