Add flags entries to test chrome OS component updates in release mode.

chrome/common/chrome_content_client.cc

Index: chrome/common/chrome_content_client.cc
diff --git a/chrome/common/chrome_content_client.cc b/chrome/common/chrome_content_client.cc
index 20ba8876bd79e7d9d3672156011d40499d53f9f0..e3e7825de940b17bc22f906597bc18c1c462a1a8 100644
--- a/chrome/common/chrome_content_client.cc
+++ b/chrome/common/chrome_content_client.cc
@@ -26,6 +26,7 @@
 #include "build/build_config.h"
 #include "chrome/common/child_process_logging.h"
 #include "chrome/common/chrome_constants.h"
+#include "chrome/common/chrome_features.h"
 #include "chrome/common/chrome_paths.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/crash_keys.h"
@@ -499,6 +500,18 @@ void ChromeContentClient::AddPepperPlugins(
   if (!sandbox::Credentials::HasFileSystemAccess())
     return;
 
+#if defined(OS_CHROMEOS)
+  // On Chrome OS, we cannot test component flash updates reliably unless we
+  // guarantee that the component updated flash plugin will be used.
+  if (base::FeatureList::IsEnabled(features::kComponentFlashOnly)) {
+    auto component_flash = base::MakeUnique<content::PepperPluginInfo>();
+    if (GetComponentUpdatedPepperFlash(component_flash.get())) {
+      plugins->push_back(*component_flash);
+    }
+    return;

[waffles, 2016/12/01 23:51:18]

I think it might be cleaner to instead do something like:

#if defined(OS_CHROMEOS)
if (base::FeatureList::IsEnabled(features::kComponentFlashOnly))
  return;
#endif

in the body of GetCommandLinePepperFlash, what do you think?

I agree it puts this override less front-and-center, but in practice
SystemPepperFlash doesn't exist on Linux, and I'm slightly worried about
short-circuiting the "fake Flash plugin" if  GetComponentUpdatedPepperFlash
returns false.

[Greg K, 2016/12/02 01:06:26]

I think you're right. The override is less obvious, but also much less prone to
break things.

+  }
+#endif  // defined(OS_CHROMEOS)
+
   auto component_flash = base::MakeUnique<content::PepperPluginInfo>();
   if (GetComponentUpdatedPepperFlash(component_flash.get()))
     flash_versions.push_back(std::move(component_flash));