Add GetCaptionButtonHeightInDIPs() method

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

Index: chrome/browser/ui/views/frame/minimize_button_metrics_win.cc
diff --git a/chrome/browser/ui/views/frame/minimize_button_metrics_win.cc b/chrome/browser/ui/views/frame/minimize_button_metrics_win.cc
index 095f2574c83c9ed91b29b7ec8972c8022cbe5d8d..8084a4c4ebf69774f201710fdc2ec512eacfeff6 100644
--- a/chrome/browser/ui/views/frame/minimize_button_metrics_win.cc
+++ b/chrome/browser/ui/views/frame/minimize_button_metrics_win.cc
@@ -4,11 +4,12 @@
 
 #include "chrome/browser/ui/views/frame/minimize_button_metrics_win.h"
 
-#include "base/logging.h"
 #include "base/i18n/rtl.h"
+#include "base/logging.h"
 #include "base/win/windows_version.h"
 #include "dwmapi.h"
 #include "ui/base/win/shell.h"
+#include "ui/display/display.h"
 #include "ui/display/win/dpi.h"
 #include "ui/display/win/screen_win.h"
 #include "ui/gfx/geometry/point.h"
@@ -52,6 +53,28 @@ MinimizeButtonMetrics::MinimizeButtonMetrics()
 MinimizeButtonMetrics::~MinimizeButtonMetrics() {
 }
 
+// static
+int MinimizeButtonMetrics::GetCaptionButtonHeightInDIPs() {
+  // At DPI scaling settings other than 100% the result won't be exactly right.
+  // TODO: return a more accurate approximation [http://crbug.com/716365]
+
+  // SM_CYSIZE returns the caption button height, but to get the full height
+  // from the top of the window we add SM_CYSIZEFRAME.
+  int cysize = GetSystemMetrics(SM_CYSIZE);
+  int cysizeframe = GetSystemMetrics(SM_CYSIZEFRAME);

[Peter Kasting, 2017/05/05 22:41:01]

Nit: Dunno if this would be clearer if these were |caption_height| and
|frame_thickness| or something.  Also these could optionally be declared const.

[emx, 2017/05/09 09:37:58]

Done.

+
+  // The result of GetSystemMetrics depends on the scale factor of the primary
+  // display. Divide the sum by that to convert to DIPs. (Converting SM_CYSIZE
+  // and SM_CYSIZEFRAME to DIPs individually adds a bigger rounding error.)
+  float primary_device_scale_factor =
+      display::Screen::GetScreen()->GetPrimaryDisplay().device_scale_factor();
+  float height_dips = (cysize + cysizeframe) / primary_device_scale_factor;
+
+  // Testing shows that floor() gives a more accurate approximation than
+  // round() here.
+  return std::floor(height_dips);
+}
+
 void MinimizeButtonMetrics::Init(HWND hwnd) {
   DCHECK(!hwnd_);
   hwnd_ = hwnd;
@@ -123,7 +146,7 @@ int MinimizeButtonMetrics::GetMinimizeButtonOffsetForWindow() const {
     TITLEBARINFOEX titlebar_info = {0};
     titlebar_info.cbSize = sizeof(TITLEBARINFOEX);
     SendMessage(hwnd_, WM_GETTITLEBARINFOEX, 0,
-                reinterpret_cast<WPARAM>(&titlebar_info));
+                reinterpret_cast<LPARAM>(&titlebar_info));
 
     // Under DWM WM_GETTITLEBARINFOEX won't return the right thing until after
     // WM_NCACTIVATE (maybe it returns classic values?). In an attempt to