media: Enable encrypted media content browsertests when MojoCdm is used

media/base/key_systems.cc

Index: media/base/key_systems.cc
diff --git a/media/base/key_systems.cc b/media/base/key_systems.cc
index f71dae2f18c93cac2395f7b9590693bf63eb4ff4..2bd244a1e38c2da85b2990324da9e65a71a7788d 100644
--- a/media/base/key_systems.cc
+++ b/media/base/key_systems.cc
@@ -19,6 +19,7 @@
 #include "media/base/key_system_names.h"
 #include "media/base/key_system_properties.h"
 #include "media/base/media.h"
+#include "media/base/media_switches.h"
 #include "ppapi/features/features.h"
 #include "media/base/media_client.h"
 #include "third_party/widevine/cdm/widevine_cdm_common.h"
@@ -351,6 +352,33 @@ void KeySystemsImpl::UpdateSupportedKeySystems() {
   AddSupportedKeySystems(&key_systems_properties);
 }
 
+// Returns whether distinctive identifiers and persistent state can be reliably
+// blocked for |properties| (and therefore be safely configurable).
+static bool CanBlock(const KeySystemProperties& properties) {
+#if BUILDFLAG(ENABLE_PEPPER_CDMS)
+  // Distinctive identifiers and persistent state can be reliably blocked for
+  // Pepper-hosted key systems.
+  DCHECK_EQ(properties.UseAesDecryptor(), properties.GetPepperType().empty());
+  if (!properties.GetPepperType().empty())
+    return true;
+#endif
+
+  // When AesDecryptor is used, we are sure we can block.
+  if (properties.UseAesDecryptor())
+    return true;
+
+  // For External Clear Key, it is either implemented as a pepper CDM (Clear Key
+  // CDM), which is covered above, or by using AesDecryptor remotely, e.g. via
+  // MojoCdm. In both cases, we can block. This is only used for testing.
+  if (base::FeatureList::IsEnabled(media::kExternalClearKeyForTesting) &&
+      IsExternalClearKey(properties.GetKeySystemName()))
+    return true;
+
+  // For other platforms assume the CDM can and will do anything. So we cannot
+  // block.
+  return false;
+}
+
 void KeySystemsImpl::AddSupportedKeySystems(
     std::vector<std::unique_ptr<KeySystemProperties>>* key_systems) {
   DCHECK(thread_checker_.CalledOnValidThread());
@@ -399,23 +427,7 @@ void KeySystemsImpl::AddSupportedKeySystems(
              EmeSessionTypeSupport::SUPPORTED_WITH_IDENTIFIER);
     }
 
-    // Distinctive identifiers and persistent state can only be reliably blocked
-    // (and therefore be safely configurable) for Pepper-hosted key systems. For
-    // other platforms assume the CDM can and will do anything, except for the
-    // following two cases:
-    // 1) AES decryptor, and
-    // 2) External Clear Key key system on Android, only enabled for testing.
-    bool can_block = properties->UseAesDecryptor();
-#if BUILDFLAG(ENABLE_PEPPER_CDMS)
-    DCHECK_EQ(properties->UseAesDecryptor(),
-              properties->GetPepperType().empty());
-    if (!properties->GetPepperType().empty())
-      can_block = true;
-#elif defined(OS_ANDROID)
-    if (IsExternalClearKey(properties->GetKeySystemName()))
-      can_block = true;
-#endif
-    if (!can_block) {
+    if (!CanBlock(*properties)) {
       DCHECK(properties->GetDistinctiveIdentifierSupport() ==
              EmeFeatureSupport::ALWAYS_ENABLED);
       DCHECK(properties->GetPersistentStateSupport() ==