[Mac] Improve modal sheet positioning during window resizing.

chrome/browser/ui/cocoa/constrained_window/constrained_window_sheet_controller_unittest.mm

Index: chrome/browser/ui/cocoa/constrained_window/constrained_window_sheet_controller_unittest.mm
diff --git a/chrome/browser/ui/cocoa/constrained_window/constrained_window_sheet_controller_unittest.mm b/chrome/browser/ui/cocoa/constrained_window/constrained_window_sheet_controller_unittest.mm
index 562155abd4de55f9e43a5926214e5d49bb2bcd11..93e6b8e52823c9fabc80f28803e2f2da24fb10c9 100644
--- a/chrome/browser/ui/cocoa/constrained_window/constrained_window_sheet_controller_unittest.mm
+++ b/chrome/browser/ui/cocoa/constrained_window/constrained_window_sheet_controller_unittest.mm
@@ -136,6 +136,11 @@ class ConstrainedWindowSheetControllerTest : public CocoaTest {
     EXPECT_EQ(expected_x, NSMinX(sheet_frame));
   }
 
+  CGFloat GetSheetYOffset(NSRect sheet_frame, NSView* parent_view) {
+    return NSMaxY(sheet_frame) -
+           NSMaxY(GetViewFrameInScreenCoordinates(parent_view));
+  }
+
   base::scoped_nsobject<NSWindow> sheet_window_;
   base::scoped_nsobject<CustomConstrainedWindowSheet> sheet_;
   base::scoped_nsobject<ConstrainedWindowSheetController> controller_;
@@ -254,6 +259,31 @@ TEST_F(ConstrainedWindowSheetControllerTest, ResizeHiddenSheet) {
   EXPECT_EQ(NSHeight(new_inactive_frame), NSHeight(new_active_frame));
 }
 
+// Test resizing parent window keeps the sheet anchored.
+TEST_F(ConstrainedWindowSheetControllerTest, ResizeParentWindow) {
+  [controller_ showSheet:sheet_ forParentView:active_tab_view_];
+  CGFloat sheet_offset =
+      GetSheetYOffset([sheet_window_ frame], active_tab_view_);
+
+  // Test 3x3 different parent window sizes.
+  CGFloat insets[] = {-10, 0, 10};
+  NSRect old_frame = [test_window() frame];
+
+  for (size_t x = 0; x < sizeof(insets) / sizeof(CGFloat); x++) {
+    for (size_t y = 0; y < sizeof(insets) / sizeof(CGFloat); y++) {
+      NSRect resized_frame = NSInsetRect(old_frame, insets[x], insets[y]);
+      [test_window() setFrame:resized_frame display:YES];
+      NSRect sheet_frame = [sheet_window_ frame];
+
+      // Y pos should track parent view's position.
+      EXPECT_EQ(sheet_offset, GetSheetYOffset(sheet_frame, active_tab_view_));
+
+      // X pos should be centered on parent view.
+      VerifySheetXPosition(sheet_frame, active_tab_view_);
+    }
+  }
+}
+
 // Test system sheets.
 TEST_F(ConstrainedWindowSheetControllerTest, SystemSheet) {
   base::scoped_nsobject<ConstrainedWindowSystemSheetTest> system_sheet(