aura: Draw persistent borders around browser windows.

This makes BrowserNonClientFrameViewAura's translucent gray
background always stick out a bit beyond the sides and
bottom of windows, instead of just peeking out when the user
hovers for resizing.

I originally added a separate view for this, but it looked
strange since Chrome already draws a shadow along the top of
the tab strip.

BUG=101977
TEST=manual

Review URL: http://codereview.chromium.org/8343066

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@107823 0039d316-1c4b-4281-b951-d872f2087c98

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

@@ -35,6 +35,10 @@ const int kTopBorderThickness = 4;
 // background at start of slide-in animation.
 const int kFrameBackgroundTopOffset = 25;
 
+// Width of a persistent border that we show around the window (using
+// FrameBackground) even when the resize border isn't visible.
+const int kPersistentBorderThickness = 2;
+
 // The color used to fill the frame.  Opacity is handled in the layer.
 const SkColor kFrameColor = SK_ColorBLACK;
 // Radius of rounded rectangle corners.
@@ -301,10 +305,11 @@ gfx::Rect BrowserNonClientFrameViewAura::GetFrameBackgroundBounds(
     show_top = true;
   gfx::Rect target = bounds();
   // Inset the sides that are not showing.
-  target.Inset((show_left ? 0 : kResizeBorderThickness),
-               (show_top ? 0 : kTopBorderThickness + kFrameBackgroundTopOffset),
-               (show_right ? 0 : kResizeBorderThickness),
-               (show_bottom ? 0 : kResizeBorderThickness));
+  target.Inset(
+      (show_left ? 0 : kResizeBorderThickness - kPersistentBorderThickness),
+      (show_top ? 0 : kTopBorderThickness + kFrameBackgroundTopOffset),
+      (show_right ? 0 : kResizeBorderThickness - kPersistentBorderThickness),
+      (show_bottom ? 0 : kResizeBorderThickness - kPersistentBorderThickness));
   return target;
 }