Fix a Context misuage in TabGridDialogMenuCoordinator

For devices with Api < 21, when we do v.getContext() where v is a
AppCompatImageView, we get a wrapped TintContextWrapper instead of a
normal Context. Casting TintContextWrapper to Activity will cause
crash. This CL fixes this misusage in TabGridDialogMenuCoordinator.

Bug: 1013555
Change-Id: I7e48923c319393def4a3f2dc130bd681347c35b0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1850591
Commit-Queue: Yue Zhang <yuezhanggg@chromium.org>
Reviewed-by: Wei-Yin Chen (陳威尹) <wychen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#705334}

chrome/android/features/tab_ui/java/src/org/chromium/chrome/browser/tasks/tab_management/TabGridDialogMenuCoordinator.java

@@ -99,7 +99,7 @@ public class TabGridDialogMenuCoordinator {
             mMenuWindow.dismiss();
         });
 
-        View decorView = ((Activity) mContext).getWindow().getDecorView();
+        View decorView = ((Activity) contentView.getContext()).getWindow().getDecorView();
         ViewRectProvider rectProvider = new ViewRectProvider(anchorView);
         Rect rect = new Rect();
         decorView.getWindowVisibleDisplayFrame(rect);