Add flag metadata for mash and ash touch debugging

* mash and single-process-mash are under active development
* show-taps and touch-hud-debug are used by developers for touch screen
  debugging

Bug: none
Change-Id: Ic4ce5ff34dd03f270ccfbe645dc321d7ed9b8b28
Reviewed-on: https://chromium-review.googlesource.com/c/1350963Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610966}

chrome/browser/flag-metadata.json

@@ -2375,8 +2375,8 @@
   },
   {
     "name": "mash",
-    // "owners": [ "your-team" ],
-    "expiry_milestone": 76
+    "owners": [ "mustash-team@google.com" ],
+    "expiry_milestone": 79
   },
   {
     "name": "material-design-ink-drop-animation-speed",
@@ -2930,13 +2930,13 @@
   },
   {
     "name": "show-taps",
-    // "owners": [ "your-team" ],
-    "expiry_milestone": 76
+    "owners": [ "//ash/OWNERS" ],
+    "expiry_milestone": -1
   },
   {
     "name": "show-touch-hud",
-    // "owners": [ "your-team" ],
-    "expiry_milestone": 76
+    "owners": [ "//ash/OWNERS" ],
+    "expiry_milestone": -1
   },
   {
     "name": "silent-debugger-extension-api",
@@ -2960,7 +2960,7 @@
   },
   {
     "name": "single-process-mash",
-    // "owners": [ "your-team" ],
+    "owners": [ "mustash-team@google.com" ],
     "expiry_milestone": 76
   },
   {