flags: assign ChromeOS gfx flags

This change assigns:
  enable-explicit-dma-fences
  overlay-strategies
  tint-gl-composited-content
to chromeos-gfx@google.com and marks them all as non-expiring. These flags are
used for graphics debugging in ChromeOS production builds.

Bug: None
Change-Id: I062dd408c8b2a2bd814798227e1ad41a1e2c7692
Reviewed-on: https://chromium-review.googlesource.com/c/1486872
Auto-Submit: Elly Fong-Jones <ellyjones@chromium.org>
Commit-Queue: Daniele Castagna <dcastagna@chromium.org>
Reviewed-by: Daniele Castagna <dcastagna@chromium.org>
Cr-Commit-Position: refs/heads/master@{#635178}

chrome/browser/flag-metadata.json

@@ -549,8 +549,10 @@
   },
   {
     "name": "enable-explicit-dma-fences",
-    "owners": [ "chromeos-gfx" ],
-    "expiry_milestone": 76
+    "owners": [ "chromeos-gfx@google.com" ],
+    // This flag is used for QA & debugging on ChromeOS, which has no way to
+    // customize switches.
+    "expiry_milestone": -1
   },
   {
     "name": "disable-hosted-app-shim-creation",
@@ -2641,8 +2643,10 @@
   },
   {
     "name": "overlay-strategies",
-    // "owners": [ "your-team" ],
-    "expiry_milestone": 76
+    "owners": [ "chromeos-gfx@google.com" ],
+    // This flag is used for QA & debugging on ChromeOS, which has no way to
+    // customize switches.
+    "expiry_milestone": -1
   },
   {
     "name": "overscroll-history-navigation",
@@ -2984,8 +2988,10 @@
   },
   {
     "name": "tint-gl-composited-content",
-    // "owners": [ "your-team" ],
-    "expiry_milestone": 76
+    "owners": [ "chromeos-gfx@google.com" ],
+    // This flag is used for QA & development on ChromeOS, which has no way to
+    // customize switches.
+    "expiry_milestone": -1
   },
   {
     "name": "top-chrome-touch-ui",