Exclude caption button bounds from non-client frame hit testing

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

Index: chrome/browser/ui/views/frame/glass_browser_frame_view.cc
diff --git a/chrome/browser/ui/views/frame/glass_browser_frame_view.cc b/chrome/browser/ui/views/frame/glass_browser_frame_view.cc
index 64f28ac79fffb97eb8023698a873f66fa1ab2cc2..b8700b63d186c9aacb152a20c60a2da9b321d764 100644
--- a/chrome/browser/ui/views/frame/glass_browser_frame_view.cc
+++ b/chrome/browser/ui/views/frame/glass_browser_frame_view.cc
@@ -4,6 +4,7 @@
 
 #include "chrome/browser/ui/views/frame/glass_browser_frame_view.h"
 
+#include <dwmapi.h>
 #include <utility>
 
 #include "base/strings/utf_string_conversions.h"
@@ -28,6 +29,7 @@
 #include "ui/base/theme_provider.h"
 #include "ui/display/win/dpi.h"
 #include "ui/gfx/canvas.h"
+#include "ui/gfx/geometry/dip_util.h"
 #include "ui/gfx/icon_util.h"
 #include "ui/gfx/image/image.h"
 #include "ui/gfx/scoped_canvas.h"
@@ -70,6 +72,9 @@ const int kNewTabCaptionMaximizedSpacing = 16;
 // TODO(bsep): Windows 10 caption buttons look very different and we would like
 // the profile switcher button to match on that platform.
 const int kProfileSwitcherButtonHeight = 20;
+// There is a small one-pixel strip right above the caption buttons in which the
+// resize border "peeks" through.
+const int kCaptionButtonTopInset = 1;
 
 // Converts the |image| to a Windows icon and returns the corresponding HICON
 // handle. |image| is resized to desired |width| and |height| if needed.
@@ -245,6 +250,32 @@ int GlassBrowserFrameView::NonClientHitTest(const gfx::Point& point) {
   if (frame_component != HTNOWHERE)
     return frame_component;
 
+  // On Windows 8+, the caption buttons are almost butted up to the top right
+  // corner of the window. This code ensures the mouse isn't set to a size
+  // cursor while hovering over the caption buttons, thus giving the incorrect
+  // impression that the user can resize the window.
+  if (base::win::GetVersion() >= base::win::VERSION_WIN8) {
+    RECT button_bounds = {0};
+    if (SUCCEEDED(DwmGetWindowAttribute(views::HWNDForWidget(frame()),
+                                        DWMWA_CAPTION_BUTTON_BOUNDS,
+                                        &button_bounds,
+                                        sizeof(button_bounds)))) {
+      gfx::Rect buttons = gfx::ConvertRectToDIP(display::win::GetDPIScale(),
+                                                gfx::Rect(button_bounds));
+      // Even though the tiny area above the caption buttons is very difficult
+      // to hit, this ensures behavioral consistency with other top-level
+      // windows. It is worth noting that this area is the same size (1px)
+      // regardless of the current scale factor. For that reason the rect is
+      // inset after it is adjusted for the device scale. Even so, this is less
+      // than ideal since conversion to DIPs may lose some precision. Given
+      // that the API doesn't take that into account, at this point this is the
+      // best we can do.

[Peter Kasting, 2016/07/20 18:47:44]

Nit: This still reads pretty confusingly to me.  What do you think of this?:

The sizing region at the window edge is 1 px regardless of scale factor.  But if
we inset by 1 before converting to DIPs, the precision loss might eliminate this
region entirely.  The best we can do is to inset after conversion, which
guarantees we'll show the resize cursor when resizing is possible, at the cost
of also showing it over the portion of the DIP that isn't the outermost pixel.

+      buttons.Inset(0, kCaptionButtonTopInset, 0, 0);
+      if (buttons.Contains(point))
+        return HTNOWHERE;
+    }
+  }
+
   int top_border_thickness = FrameTopBorderThickness(false);
   // We want the resize corner behavior to apply to the kResizeCornerWidth
   // pixels at each end of the top and bottom edges.  Because |point|'s x