Plumb base::Feature field trial association to renderers.

This CL makes the FeatureList command-line initialization code
support an optional FieldTrial name for each feature that will
be associated with the feature override when specified. Also
changes the code that generates this command-line to also
include this name.

With this change, renderers will be launched with this
association specified on the command-line, so that querying
a Feature in the renderer only that's associated with a field
trial will result in that trial being activated (and sync'd with
the browser process by the existing mechanism).

Depends on:
https://codereview.chromium.org/1471693007

BUG=561077

Review URL: https://codereview.chromium.org/1484483002

Cr-Commit-Position: refs/heads/master@{#362343}

1 files changed, 14 insertions, 1 deletions

diff --git a/base/feature_list_unittest.cc b/base/feature_list_unittest.cc
index 414c74a..29c1f16 100644
--- a/base/feature_list_unittest.cc
+++ b/base/feature_list_unittest.cc
@@ -335,8 +335,21 @@ TEST_F(FeatureListTest, GetFeatureOverrides) {
   std::string disable_features;
   FeatureList::GetInstance()->GetFeatureOverrides(&enable_features,
                                                   &disable_features);
-  EXPECT_EQ("A,OffByDefault,X", SortFeatureListString(enable_features));
+  EXPECT_EQ("A,OffByDefault<Trial,X", SortFeatureListString(enable_features));
   EXPECT_EQ("D", SortFeatureListString(disable_features));
 }
 
+TEST_F(FeatureListTest, InitializeFromCommandLine_WithFieldTrials) {
+  ClearFeatureListInstance();
+  FieldTrialList field_trial_list(nullptr);
+  FieldTrialList::CreateFieldTrial("Trial", "Group");
+  scoped_ptr<FeatureList> feature_list(new FeatureList);
+  feature_list->InitializeFromCommandLine("A,OffByDefault<Trial,X", "D");
+  RegisterFeatureListInstance(feature_list.Pass());
+
+  EXPECT_FALSE(FieldTrialList::IsTrialActive("Trial"));
+  EXPECT_TRUE(FeatureList::IsEnabled(kFeatureOffByDefault));
+  EXPECT_TRUE(FieldTrialList::IsTrialActive("Trial"));
+}
+
 }  // namespace base