Add a group policy for hardware acceleration.

chrome/test/data/policy/policy_test_cases.json

 {
   "-- Template --": {
     "intro": "Top-level entries map a policy name to its test parameters, described below. The name of the top level entry should be of the form <policy name>[.suffix]. The optional suffix is used for defining multiple test cases for a single policy.",
 
     "os": ["List of operating systems that support this policy. Valid values:", "win", "linux", "mac", "chromeos", "Defaults to empty if not specified."],
     "official_only": "Whether this policy exists in official builds only. Defaults to |false| if not specified.",
     "can_be_recommended": "Whether a recommended value may be set for the policy. Defaults to |false| if not specified.",
     "test_policy": "A policy dictionary that should make the preferences affected by this policy become policy-controlled. Usually just sets the current policy. Defaults to an empty dictionary if not specified.",
     "note": "If the policy affects any preferences, the following array should be specified with one entry per such preference.",
     "pref_mappings": [
@@ skipping 2225 matching lines @@
     "os": ["win", "linux", "mac", "chromeos"],
     "test_policy": { "SSLErrorOverrideAllowed": true },
     "pref_mappings": [
       { "pref": "ssl.error_override_allowed" }
     ]
   },
 
   "KeyPermissions": {
   },
 
+  "HardwareAccelerationModeEnabled": {
+    "os": ["win", "linux", "mac", "chromeos", "android"],
+    "test_policy": { "HardwareAccelerationModeEnabled": false },
+    "pref_mappings": [
+      { "pref": "hardware_acceleration_mode.enabled" }

[bartfab (slow), 2015/07/01 09:16:54]

Since this pref is exposed in chrome://settings, please add a controlled setting
indicator for it and extend the test case accordingly.

[Zhenyao Mo, 2015/07/01 17:56:07]

I read the documentation and also examples in this file, but I still have no
good idea how to set up indicator_test_setup_js and indicator_selector.  Can you
give me a hand here?  The settings is Advanced Settings -> System -> Use
hardware acceleration when available.

[bartfab (slow), 2015/07/08 12:40:33]

You do not need to worry about |indicator_test_setup_js| and
|indicator_selector|. These are for special cases only where our default
mechanisms do not work. In your case, the default mechanisms should work:

1) Add a controlled-setting-indicator element to the HTML page that contains the
hardware acceleration setting and set up its attributes so that it listens for
the right pref.
2) Add one or more |indicator_tests|. They will locate the correct indicator
automatically.

+    ]
+  },
+
   "----- Chrome OS device policies ---------------------------------------": {},
 
   "DevicePolicyRefreshRate": {
     "os": ["chromeos"],
     "test_policy": { "DevicePolicyRefreshRate": 300000 },
     "pref_mappings": [
       { "pref": "policy.device_refresh_rate",
         "local_state": true }
     ]
   },
@@ skipping 213 matching lines @@
 
   "AdditionalLaunchParameters": {
   },
 
   "SuppressChromeFrameTurndownPrompt": {
   },
 
   "SkipMetadataCheck": {
   }
 }