Add check_gn_headers.py to find missing headers in GN

testing/buildbot/chromium.linux.json

 {
   "Android Arm64 Builder (dbg)": {
     "additional_compile_targets": [
       "all"
     ]
   },
   "Android Builder": {
     "additional_compile_targets": [
       "cronet_test_instrumentation_apk",
       "system_webview_apk"
@@ skipping 1275 matching lines @@
       },
       {
         "test": "ui_junit_tests"
       },
       {
         "test": "webapk_client_junit_tests"
       },
       {
         "test": "webapk_shell_apk_junit_tests"
       }
+    ],
+    "scripts": [
+      {
+        "name": "check_gn_headers",
+        "script": "check_gn_headers.py"
+      }

[Dirk Pranke, 2017/01/09 06:47:49]

As I noted in the bug, it's not immediately clear how to make this work as a
test step on the bots. Let's leave this file unmodified and leave the
//testing/scripts/check_gn_headers.py file out of this CL, so that we can land
the rest.

[wychen, 2017/01/09 13:14:53]

I've removed them from this CL.

According to my design doc, the stale .d file can be eliminated if this checking
is only done after a full compile. As for the skipped analysis, even though
temporary regression could happen, new errors would eventually be discovered.

Quote: "Note that it can go wrong only if a new header is exclusively included
by whitelisted headers. If the new header is also included by any cc files, “gn
analyze” would trigger compilation. Therefore, the error scenario should be
infrequent enough so that sheriffs could revert the culprit without too much
difficulty."

Do you think it's better to wait until we have PRESUBMIT heuristics to
complement the checking on CQ?

     ]
   },
   "Android Tests (dbg)": {
     "gtest_tests": [
       {
         "override_compile_targets": [
           "android_webview_test_apk"
         ],
         "override_isolate_target": "android_webview_test_apk",
         "swarming": {
@@ skipping 1255 matching lines @@
       },
       {
         "test": "ui_junit_tests"
       },
       {
         "test": "webapk_client_junit_tests"
       },
       {
         "test": "webapk_shell_apk_junit_tests"
       }
+    ],
+    "scripts": [
+      {
+        "name": "check_gn_headers",
+        "script": "check_gn_headers.py"
+      }
     ]
   },
   "Blimp Linux (dbg)": {
     "gtest_tests": [
       {
         "swarming": {
           "can_use_on_swarming_builders": true
         },
         "test": "blimp_browsertests"
       },
@@ skipping 834 matching lines @@
         "override_compile_targets": [
           "telemetry_unittests_run"
         ],
         "swarming": {
           "can_use_on_swarming_builders": true
         }
       }
     ],
     "scripts": [
       {
+        "name": "check_gn_headers",
+        "script": "check_gn_headers.py"
+      },
+      {
         "name": "checkdeps",
         "script": "checkdeps.py"
       },
       {
         "name": "checkperms",
         "script": "checkperms.py"
       },
       {
         "name": "nacl_integration",
         "script": "nacl_integration.py"
@@ skipping 542 matching lines @@
         "override_compile_targets": [
           "telemetry_unittests_run"
         ],
         "swarming": {
           "can_use_on_swarming_builders": true
         }
       }
     ],
     "scripts": [
       {
+        "name": "check_gn_headers",
+        "script": "check_gn_headers.py"
+      },
+      {
         "name": "nacl_integration",
         "script": "nacl_integration.py"
       }
     ]
   },
   "Linux Tests (dbg)(1)(32)": {
     "gtest_tests": [
       {
         "swarming": {
           "can_use_on_swarming_builders": true
@@ skipping 347 matching lines @@
         "override_compile_targets": [
           "telemetry_unittests_run"
         ],
         "swarming": {
           "can_use_on_swarming_builders": true
         }
       }
     ]
   }
 }