Change snasphotting API to take in a bounds Rect

chrome/browser/ui/window_snapshot/window_snapshot_mac.mm

Index: chrome/browser/ui/window_snapshot/window_snapshot_mac.mm
diff --git a/chrome/browser/ui/window_snapshot/window_snapshot_mac.mm b/chrome/browser/ui/window_snapshot/window_snapshot_mac.mm
index ab790872e0db1c88dd5602bf31d0f384e2623306..134a0deeb53ea0aaa42006168ae6d879dbe16953 100644
--- a/chrome/browser/ui/window_snapshot/window_snapshot_mac.mm
+++ b/chrome/browser/ui/window_snapshot/window_snapshot_mac.mm
@@ -14,9 +14,19 @@
 namespace browser {
 
 gfx::Rect GrabWindowSnapshot(gfx::NativeWindow window,
-    std::vector<unsigned char>* png_representation) {
+    std::vector<unsigned char>* png_representation,
+    gfx::Rect snapshot_bounds) {
   png_representation->clear();
 
+  CGRect windowRect = CGRectNUll;
+  if (!snapshot_bounds.IsEmpty()) {
+      gfx::Rect window_bounds = gfx::Rect([window frame]);
+      snapshot_bounds.Offset(window_bounds.left(), window_bounds.top());
+      windowRect = snapshot_bounds.ToCGRect();
+      DCHECK(snapshot_bounds.right() <= window_bounds.right());
+      DCHECK(snapshot_bounds.bottom() <= window_bounds.bottom()); 
+  }
+
   // Make sure to grab the "window frame" view so we get current tab +
   // tabstrip.
   NSView* view = [[window contentView] superview];