Add Keycode for keyboard paste shortcut.

The keycode for CTRL+V is needed to simulate a paste event to test whether PhishGuard captures passwords when the users pastes their password (https://chromium-review.googlesource.com/c/chromium/src/+/1576118)

Change-Id: I92b7c669232a95f29f4ae26773524e9675936f46
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1593031
Commit-Queue: Archana Simha <archanasimha@google.com>
Reviewed-by: Varun Khaneja <vakh@chromium.org>
Reviewed-by: Gary Kacmarcik <garykac@chromium.org>
Cr-Commit-Position: refs/heads/master@{#660598}

ui/events/keycodes/keyboard_codes_posix.h

@@ -47,6 +47,7 @@ enum KeyboardCode {
   VKEY_CAPITAL = 0x14,
   VKEY_KANA = 0x15,
   VKEY_HANGUL = 0x15,
+  VKEY_PASTE = 0x16,
   VKEY_JUNJA = 0x17,
   VKEY_FINAL = 0x18,
   VKEY_HANJA = 0x19,

ui/events/keycodes/keyboard_codes_win.h

@@ -27,6 +27,9 @@ enum KeyboardCode {
   VKEY_FINAL = VK_FINAL,
   VKEY_HANJA = VK_HANJA,
   VKEY_KANJI = VK_KANJI,
+  VKEY_PASTE = 0x16,  // Used to simulate CTRL+V key event
+                      // (chromium/src/ui/events/event.cc), however 0x16 is an
+                      // undefined value.
   VKEY_ESCAPE = VK_ESCAPE,
   VKEY_CONVERT = VK_CONVERT,
   VKEY_NONCONVERT = VK_NONCONVERT,