Make default media device ID salts random by default

content/browser/resource_context_impl.cc

Index: content/browser/resource_context_impl.cc
diff --git a/content/browser/resource_context_impl.cc b/content/browser/resource_context_impl.cc
index e7aa29b9570d5706018be8032db33507b15392f9..f09ac807f7834fdd03d080643cbb5a5aab4e02fe 100644
--- a/content/browser/resource_context_impl.cc
+++ b/content/browser/resource_context_impl.cc
@@ -6,9 +6,13 @@
 
 #include <stdint.h>
 
+#include <string>
+
+#include "base/base64.h"
 #include "base/bind.h"
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
+#include "base/rand_util.h"
 #include "content/browser/blob_storage/chrome_blob_storage_context.h"
 #include "content/browser/loader/resource_dispatcher_host_impl.h"
 #include "content/browser/loader/resource_request_info_impl.h"
@@ -30,15 +34,14 @@ const char kBlobStorageContextKeyName[] = "content_blob_storage_context";
 const char kStreamContextKeyName[] = "content_stream_context";
 const char kURLDataManagerBackendKeyName[] = "url_data_manager_backend";
 
-// Used by the default implementation of GetMediaDeviceIDSalt, below.
-std::string ReturnEmptySalt() {
-  return std::string();
+std::string GetSalt(const std::string& salt) {
+  return salt;
 }
 
 }  // namespace
 
-
-ResourceContext::ResourceContext() {
+ResourceContext::ResourceContext()
+    : media_device_id_salt_(CreateRandomMediaDeviceIDSalt()) {
   ResourceDispatcherHostImpl* rdhi = ResourceDispatcherHostImpl::Get();
   if (rdhi) {
     BrowserThread::PostTask(
@@ -60,7 +63,7 @@ ResourceContext::~ResourceContext() {
 }
 
 ResourceContext::SaltCallback ResourceContext::GetMediaDeviceIDSalt() {
-  return base::Bind(&ReturnEmptySalt);
+  return base::Bind(GetSalt, media_device_id_salt_);
 }
 
 std::unique_ptr<net::ClientCertStore> ResourceContext::CreateClientCertStore() {
@@ -76,6 +79,14 @@ void ResourceContext::CreateKeygenHandler(
       new net::KeygenHandler(key_size_in_bits, challenge_string, url)));
 }
 
+// static
+std::string ResourceContext::CreateRandomMediaDeviceIDSalt() {
+  std::string salt;
+  base::Base64Encode(base::RandBytesAsString(16), &salt);
+  DCHECK(!salt.empty());
+  return salt;
+}
+
 ChromeBlobStorageContext* GetChromeBlobStorageContextForResourceContext(
     const ResourceContext* resource_context) {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);