[Dice] Change drop down arrow for DiceSigninButton

The DiceSigninButton should show an arrow pointing
downwards instead of to the right. This CL fixes
this.

Screenshot from before:
https://drive.google.com/file/d/13T9Wv99rezwCDQ9EnW3drrSmrGIoAtor/view?usp=sharing
Screenshot from after:
https://drive.google.com/file/d/1d9_N_IOvjLhohMrm4eEWE8-4ElaC7qBv/view?usp=sharing

Bug: 812283
Change-Id: Ic0c2229c24532f45fbdb236fe222505cd36cd572
Reviewed-on: https://chromium-review.googlesource.com/924070Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Thomas Tangl <tangltom@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537621}

chrome/app/vector_icons/signin_button_drop_down_arrow.icon

@@ -3,8 +3,8 @@
 // found in the LICENSE file.
 
 CANVAS_DIMENSIONS, 24,
-MOVE_TO, 8, 5,
-R_V_LINE_TO, 14,
-R_LINE_TO, 11, -7,
+MOVE_TO, 5, 8,
+R_H_LINE_TO, 14,
+R_LINE_TO, -7, 11,
 CLOSE,
 END