WATCHLISTS: Add media_gpu_cros and homogenised with some existing ones

This CL:
- Adds a media_gpu_cros target, with the appropriate folders to watch
 and directed to the similarly named mailing list.
- Takes the chance to rename other similar variables, |media_win| and
 |vaapi|, so they start with media_gpu_ and are therefore grouped
 together.

Tested it with statements like:
~/p/depot_tools/watchlists.py media/mojo/clients/mojo_video_encode_accelerator.h
~/p/depot_tools/watchlists.py media/gpu/h264_decoder.h

to verify it.

Change-Id: I790a88bf109137a7119a164fa98b0c754e342f99
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1993143
Reviewed-by: Jao-ke Chin-Lee <jchinlee@chromium.org>
Commit-Queue: Miguel Casas <mcasas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#729871}

WATCHLISTS

@@ -1217,6 +1217,19 @@
     'media_gpu': {
       'filepath': 'media/gpu/',
     },
+    'media_gpu_cros': {
+      'filepath': 'media/gpu/chromeos'\
+                  '|media/gpu/vaapi'\
+                  '|media/gpu/v4l2'\
+                  '|media/gpu/.*\.(cc|h)$'\
+                  '|media/mojo/(clients|mojom|test|services)/.*accelerator.*'
+    },
+    'media_gpu_vaapi': {
+      'filepath': 'media/gpu/vaapi',
+    },
+    'media_gpu_win': {
+      'filepath': 'media/gpu/windows/'
+    },
     'media_mojo': {
       'filepath': 'media/mojo/'
     },
@@ -1246,9 +1259,6 @@
                   '|chrome/test/media_router/' \
                   '|chrome/utility/media_router/'
     },
-    'media_win': {
-      'filepath': 'media/gpu/windows/'
-    },
     'message_loop': {
       'filepath': 'base/message_'
     },
@@ -1857,9 +1867,6 @@
     'usb': {
       'filepath': '/usb/',
     },
-    'vaapi': {
-      'filepath': 'media/gpu/vaapi',
-    },
     'version_assembly': {
       'filepath': 'chrome/app/version_assembly',
     },
@@ -2519,6 +2526,9 @@
     'media_galleries': ['thestig@chromium.org',
                         'tommycli@chromium.org'],
     'media_gpu': ['hiroh+watch@chromium.org'],
+    'media_gpu_cros': ['media-cros-reviews@chromium.org'],
+    'media_gpu_vaapi': ['vaapi-reviews@chromium.org'],
+    'media_gpu_win': ['media-win-reviews@chromium.org'],
     'media_mojo': ['alokp+watch@chromium.org',
                    'xhwang+watch@chromium.org'],
     'media_recorder': ['emircan+watch+mediarecorder@chromium.org',
@@ -2529,7 +2539,6 @@
     'media_router': ['mfoltz+watch@chromium.org',
                      'pthatcher+watch@chromium.org',
                      'takumif+watch@chromium.org'],
-    'media_win': ['media-win-reviews@chromium.org'],
     'message_loop': ['sadrul@chromium.org'],
     'metrics': ['asvitkine+watch@chromium.org'],
     'metrics_perf': ['cwp-reviews+chromium@google.com'],
@@ -2760,7 +2769,6 @@
     'unified_consent': ['wfh+watch@chromuium.org'],
     'usb': ['mattreynolds+watch@chromium.org',
             'odejesush+watch@chromium.org'],
-    'vaapi': ['vaapi-reviews@chromium.org'],
     'version_assembly': ['caitkp+watch@chromium.org',
                          'gab+watch@chromium.org'],
     'video': ['posciak+watch@chromium.org'],