media: Add a feature for CdmHostVerification

By default it's enabled. No effect if ENABLE_CDM_HOST_VERIFICATION
buildflag is false.

To disable this feature for testing, type the following in the command
line:
  --disable-features=CdmHostVerification

Bug: 658036
Test: Manually tested with the feature disabled
Change-Id: Ia2d077436a1a8445aec29163a88d1bb4539c4811
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2036257Reviewed-by: John Rummell <jrummell@chromium.org>
Commit-Queue: Xiaohan Wang <xhwang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#738795}

media/base/media_switches.cc

@@ -253,6 +253,11 @@ const base::Feature kUseAndroidOverlayAggressively{
 const base::Feature kBackgroundVideoPauseOptimization{
     "BackgroundVideoPauseOptimization", base::FEATURE_ENABLED_BY_DEFAULT};
 
+// CDM host verification is enabled by default. Can be disabled for testing.
+// Has no effect if ENABLE_CDM_HOST_VERIFICATION buildflag is false.
+const base::Feature kCdmHostVerification{"CdmHostVerification",
+                                         base::FEATURE_ENABLED_BY_DEFAULT};
+
 // Make MSE garbage collection algorithm more aggressive when we are under
 // moderate or critical memory pressure. This will relieve memory pressure by
 // releasing stale data from MSE buffers.

media/base/media_switches.h

@@ -106,6 +106,7 @@ MEDIA_EXPORT extern const base::Feature kAutoplayDisableSettings;
 MEDIA_EXPORT extern const base::Feature kAutoplayWhitelistSettings;
 MEDIA_EXPORT extern const base::Feature kBackgroundVideoPauseOptimization;
 MEDIA_EXPORT extern const base::Feature kBresenhamCadence;
+MEDIA_EXPORT extern const base::Feature kCdmHostVerification;
 MEDIA_EXPORT extern const base::Feature kD3D11PrintCodecOnCrash;
 MEDIA_EXPORT extern const base::Feature kD3D11VideoDecoder;
 MEDIA_EXPORT extern const base::Feature kD3D11VideoDecoderIgnoreWorkarounds;

media/cdm/cdm_module.cc

@@ -13,6 +13,8 @@
 #include "components/crash/core/common/crash_key.h"
 
 #if BUILDFLAG(ENABLE_CDM_HOST_VERIFICATION)
+#include "base/feature_list.h"
+#include "media/base/media_switches.h"
 #include "media/cdm/cdm_host_files.h"
 #endif  // BUILDFLAG(ENABLE_CDM_HOST_VERIFICATION)
 
@@ -180,6 +182,7 @@ bool CdmModule::Initialize(const base::FilePath& cdm_path) {
 #endif  // defined(OS_WIN)
 
 #if BUILDFLAG(ENABLE_CDM_HOST_VERIFICATION)
+  if (base::FeatureList::IsEnabled(media::kCdmHostVerification))
     InitCdmHostVerification(library_.get(), cdm_path_, cdm_host_file_paths);
 #endif  // BUILDFLAG(ENABLE_CDM_HOST_VERIFICATION)