Make FeatureList override state be plumbed to renderer processes.

Previously, the browser copied over verbatim the --enable-features
and --disable-features command-line. However, this wouldn't have
captured overrides as a result of field trials. This change updates
the logic to include those in the list. The new logic will continue
to work for plumbing command-lines as well, since those are also
registered using the override mechanism.

Note: There's still some follow-up work that needs to be done to
plumb the FieldTrial association state (so that a FieldTrial that's
not active will get activated in the renderer if the associated
Feature is queried). But this can be supported in a follow-up CL
that builds on top of this one.

BUG=561077

Review URL: https://codereview.chromium.org/1471693007

Cr-Commit-Position: refs/heads/master@{#362294}

1 files changed, 21 insertions, 2 deletions

diff --git a/content/browser/renderer_host/render_process_host_impl.cc b/content/browser/renderer_host/render_process_host_impl.cc
index 91e438f..f88d475 100644
--- a/content/browser/renderer_host/render_process_host_impl.cc
+++ b/content/browser/renderer_host/render_process_host_impl.cc
@@ -17,6 +17,7 @@
 #include "base/callback.h"
 #include "base/command_line.h"
 #include "base/debug/dump_without_crashing.h"
+#include "base/feature_list.h"
 #include "base/files/file.h"
 #include "base/lazy_instance.h"
 #include "base/location.h"
@@ -433,6 +434,24 @@ std::string UintVectorToString(const std::vector<unsigned>& vector) {
   return str;
 }
 
+// Copies kEnableFeatures and kDisableFeatures to the renderer command line.
+// Generates them from the FeatureList override state, to take into account
+// overrides from FieldTrials.
+void CopyEnableDisableFeatureFlagsToRenderer(base::CommandLine* renderer_cmd) {
+  std::string enabled_features;
+  std::string disabled_features;
+  base::FeatureList::GetInstance()->GetFeatureOverrides(&enabled_features,
+                                                        &disabled_features);
+  if (!enabled_features.empty()) {
+    renderer_cmd->AppendSwitchASCII(switches::kEnableFeatures,
+                                    enabled_features);
+  }
+  if (!disabled_features.empty()) {
+    renderer_cmd->AppendSwitchASCII(switches::kDisableFeatures,
+                                    disabled_features);
+  }
+}
+
 }  // namespace
 
 RendererMainThreadFactoryFunction g_renderer_main_thread_factory = NULL;
@@ -1306,7 +1325,6 @@ void RenderProcessHostImpl::PropagateBrowserCommandLineToRenderer(
     switches::kDisableDisplayList2dCanvas,
     switches::kDisableDistanceFieldText,
     switches::kDisableEncryptedMedia,
-    switches::kDisableFeatures,
     switches::kDisableFileSystem,
     switches::kDisableGestureRequirementForMediaPlayback,
     switches::kDisableGpuCompositing,
@@ -1345,7 +1363,6 @@ void RenderProcessHostImpl::PropagateBrowserCommandLineToRenderer(
     switches::kEnableDistanceFieldText,
     switches::kEnableExperimentalCanvasFeatures,
     switches::kEnableExperimentalWebPlatformFeatures,
-    switches::kEnableFeatures,
     switches::kEnableHeapProfiling,
     switches::kEnableGPUClientLogging,
     switches::kEnableGpuClientTracing,
@@ -1487,6 +1504,8 @@ void RenderProcessHostImpl::PropagateBrowserCommandLineToRenderer(
   renderer_cmd->CopySwitchesFrom(browser_cmd, kSwitchNames,
                                  arraysize(kSwitchNames));
 
+  CopyEnableDisableFeatureFlagsToRenderer(renderer_cmd);
+
   if (browser_cmd.HasSwitch(switches::kTraceStartup) &&
       BrowserMainLoop::GetInstance()->is_tracing_startup_for_duration()) {
     // Pass kTraceStartup switch to renderer only if startup tracing has not