Bug 1547395 - Allow specific tasks in the use-pgo field; r=tomprince

Some groups of tasks need to share the same profile data. For example,
Android PGO builds and Android Nightly builds both use the
generate-profile-android-api-16/pgo task for profile data. Previously
this was done with a text substitution, but this is a bit hacky and
doesn't easily scale with different build types.

Allowing use_pgo to be a string means we can just directly point to the
generate-profile task that contains the profile data to be used in a PGO
build.

Differential Revision: https://phabricator.services.mozilla.com/D29247

--HG--
extra : moz-landing-system : lando

taskcluster/ci/build/android.yml

@@ -384,7 +384,7 @@ android-api-16-without-google-play-services/opt:
 
 android-api-16-nightly/opt:
     description: "Android 4.0 api-16+ Nightly"
-    use-pgo: true
+    use-pgo: android-api-16/pgo
     attributes:
         nightly: true
         enable-full-crashsymbols: true

taskcluster/taskgraph/transforms/build.py

@@ -103,14 +103,18 @@ def mozconfig(config, jobs):
 @transforms.add
 def use_profile_data(config, jobs):
     for job in jobs:
-        if not job.pop('use-pgo', False):
+        use_pgo = job.pop('use-pgo', False)
+        if not use_pgo:
             yield job
             continue
 
-        # Nightlies use the same profile information as a regular PGO build.
-        name = job['name']
-        if name.endswith('-nightly/opt'):
-            name = name.replace('-nightly/opt', '/pgo')
+        # If use_pgo is True, the task uses the generate-profile task of the
+        # same name. Otherwise a task can specify a specific generate-profile
+        # task to use in the use_pgo field.
+        if use_pgo is True:
+            name = job['name']
+        else:
+            name = use_pgo
         dependencies = 'generate-profile-{}'.format(name)
         job.setdefault('dependencies', {})['generate-profile'] = dependencies
         job.setdefault('fetches', {})['generate-profile'] = ['profdata.tar.xz']