Fix ScreenCapturerMac handling of secondary configurations.

media/video/capture/screen/mac/desktop_configuration.mm

Index: media/video/capture/screen/mac/desktop_configuration.mm
diff --git a/media/video/capture/screen/mac/desktop_configuration.mm b/media/video/capture/screen/mac/desktop_configuration.mm
index 064c4efa77e1871836fbd620f3171f955c14e387..c5a6061724accfd6709515b792e6755726f5364e 100644
--- a/media/video/capture/screen/mac/desktop_configuration.mm
+++ b/media/video/capture/screen/mac/desktop_configuration.mm
@@ -21,20 +21,24 @@
 
 namespace media {
 
-MacDisplayConfiguration::MacDisplayConfiguration()
-  : id(0),
-    bounds(SkIRect::MakeEmpty()),
-    pixel_bounds(SkIRect::MakeEmpty()),
-    dip_to_pixel_scale(1.0f) {
-}
+namespace {
 
-static SkIRect NSRectToSkIRect(const NSRect& ns_rect) {
+SkIRect NSRectToSkIRect(const NSRect& ns_rect) {
   SkIRect result;
   gfx::CGRectToSkRect(NSRectToCGRect(ns_rect)).roundOut(&result);
   return result;
 }
 
-static MacDisplayConfiguration GetConfigurationForScreen(NSScreen* screen) {
+// Inverts the position of |rect| about the horizontal mid-point of |bounds|.
+// If |bounds| refers to a Cartesian coordinate space then this effectively
+// converts |rect| from Cartesian (bottom-left origin) to inverse-Cartesian
+// (top-left origin) coordinates.
+void InvertRectYOrigin(const SkIRect& bounds, SkIRect* rect) {
+  rect->setXYWH(rect->x(), bounds.top() + bounds.bottom() - rect->bottom(),
+                rect->width(), rect->height());
+}
+
+MacDisplayConfiguration GetConfigurationForScreen(NSScreen* screen) {
   MacDisplayConfiguration display_config;
 
   // Fetch the NSScreenNumber, which is also the CGDirectDisplayID.
@@ -60,17 +64,26 @@ static MacDisplayConfiguration GetConfigurationForScreen(NSScreen* screen) {
   return display_config;
 }
 
+} // namespace
+
+MacDisplayConfiguration::MacDisplayConfiguration()
+    : id(0),
+      bounds(SkIRect::MakeEmpty()),
+      pixel_bounds(SkIRect::MakeEmpty()),
+      dip_to_pixel_scale(1.0f) {
+}
+
 MacDesktopConfiguration::MacDesktopConfiguration()
-  : bounds(SkIRect::MakeEmpty()),
-    pixel_bounds(SkIRect::MakeEmpty()),
-    dip_to_pixel_scale(1.0f) {
+    : bounds(SkIRect::MakeEmpty()),
+      pixel_bounds(SkIRect::MakeEmpty()),
+      dip_to_pixel_scale(1.0f) {
 }
 
 MacDesktopConfiguration::~MacDesktopConfiguration() {
 }
 
 // static
-MacDesktopConfiguration MacDesktopConfiguration::GetCurrent() {
+MacDesktopConfiguration MacDesktopConfiguration::GetCurrent(Origin origin) {
   MacDesktopConfiguration desktop_config;
 
   NSArray* screens = [NSScreen screens];
@@ -92,6 +105,16 @@ MacDesktopConfiguration MacDesktopConfiguration::GetCurrent() {
       continue;
     }
 
+    // Mac uses Cartesian (bottom-left origin) coordinates, so if the caller
+    // wants inverse Cartesian (top-left origin), secondary monitors need
+    // their coordinates inverting relative to the primary monitor's bounds.
+    if (i > 0 && origin == TopLeftOrigin) {
+      InvertRectYOrigin(desktop_config.displays[0].bounds,
+                        &display_config.bounds);
+      InvertRectYOrigin(desktop_config.displays[0].pixel_bounds,
+                        &display_config.pixel_bounds);
+    }
+
     // Add the display to the configuration.
     desktop_config.displays.push_back(display_config);