Add GN (the build tool) to the chromium.linux buildbots and try jobs

scripts/slave/recipes/chromium_trybot.py

Index: scripts/slave/recipes/chromium_trybot.py
diff --git a/scripts/slave/recipes/chromium_trybot.py b/scripts/slave/recipes/chromium_trybot.py
index 84bc5978256d11ed7fd238a25be11adf4fbdaa44..e3feedb5a4badf04de20ad34fb7a718b077da822 100644
--- a/scripts/slave/recipes/chromium_trybot.py
+++ b/scripts/slave/recipes/chromium_trybot.py
@@ -268,6 +268,15 @@ def GenSteps(api):
   else:
     yield api.chromium.runhooks()
 
+  # TODO(dpranke): crbug.com/353690. Remove the gn-specific steps from this
+  # recipe and stand up a dedicated GN bot when the GN steps take up enough
+  # resources to be worth it. For now, we run GN and generate files into a new
+  # Debug_gn / Release_gn dir, and then run a compile in that dir.
+  gn_output_dir = api.path['slave_build'].join(api.chromium.c.BUILD_CONFIG +
+                                               '_gn')
+  should_run_gn = api.properties.get('buildername') in ('linux_chromium',
+                                                        'linux_chromium_rel')
+
   test_spec = api.step_history['read test spec'].json.output
   test_spec = [s.encode('utf-8') for s in test_spec]
 
@@ -284,7 +293,14 @@ def GenSteps(api):
                              name='compile (with patch)',
                              abort_on_failure=False,
                              can_fail_build=False)
-  if api.step_history['compile (with patch)'].retcode != 0:
+  if should_run_gn:
+    yield api.chromium.run_gn(gn_output_dir)
+    yield api.chromium.compile_with_ninja('compile (gn with patch)',
+                                          gn_output_dir)
+
+  if ((api.step_history['compile (with patch)'].retcode != 0) or
+      (should_run_gn and
+       api.step_history['compile (gn with patch)'].retcode != 0)):
     # Only use LKCR when compile fails. Note that requested specific revision
     # can still override this.
     api.gclient.set_config('chromium_lkcr')
@@ -316,6 +332,12 @@ def GenSteps(api):
                                  name='compile (with patch, lkcr, clobber)',
                                  force_clobber=True)
 
+    if should_run_gn:
+      yield api.path.rmcontents('slave gn build directory', gn_output_dir)
+      yield api.chromium.run_gn(gn_output_dir)
+      yield api.chromium.compile_with_ninja(
+          'compile (gn with patch, lkcr, clobber)', gn_output_dir)
+
   # Do not run tests if the build is already in a failed state.
   if api.step_history.failed:
     return
@@ -323,7 +345,12 @@ def GenSteps(api):
   if recipe_config['compile_only']:
     return
 
-  # TODO(phajdan.jr): Make it possible to retry telemtry tests (add JSON).
+  # TODO(dpranke): crbug.com/353690. It would be good to run gn_unittests
+  # out of the gn build dir, but we can't use runtest()
+  # because of the different output directory; this means
+  # we don't get annotations and don't get retry of the tests for free :( .
+
+  # TODO(phajdan.jr): Make it possible to retry telemetry tests (add JSON).
   yield (
     api.chromium.run_telemetry_unittests(),
     api.chromium.run_telemetry_perf_unittests(),
@@ -459,3 +486,21 @@ def GenTests(api):
     api.step_data('compile (with patch, lkcr, clobber)', retcode=1) +
     api.step_data('compile (with patch, lkcr, clobber, nuke)', retcode=1)
   )
+
+  # TODO(dpranke): crbug.com/353690.
+  # Remove this when we make GN a standalone recipe.
+  yield (
+    api.test('unittest_should_run_gn') +
+    api.properties.tryserver(buildername='linux_chromium',
+                             build_config='Debug') +
+    api.platform.name('linux') +
+    api.step_data('compile (gn with patch)')
+  )
+
+  yield (
+    api.test('unittest_should_run_gn_compile_failure') +
+    api.properties.tryserver(buildername='linux_chromium',
+                             build_config='Debug') +
+    api.platform.name('linux') +
+    api.step_data('compile (gn with patch)', retcode=1)
+  )