Creating a new RNG and replacing rand().

[ Merge of http://go/wvgerrit/84607 ]
[ Merge of http://go/wvgerrit/84608 ]

The primary goal is to replace the use of `rand()` with the random
number generators provided with the C++11 standard.

This simplified generator wraps some of the technical aspects of the
<random> library and provides an interface for uniformly distributed
integers.

As part of the `rand()` purge in the CDM, all uses of the C random int
function in `core()` have been removed.  Places that previously used
`rand()` now use `CdmRandom` facilities.

Test: Linux unittest and Android unittest
Bug: 130680365
Change-Id: Ica383870536ed462dbb80e630c2d66845e38b937

libwvdrmengine/cdm/core/src/cdm_engine.cpp

@@ -12,6 +12,7 @@
 #include <memory>
 #include <sstream>
 
+#include "cdm_random.h"
 #include "cdm_session.h"
 #include "cdm_session_map.h"
 #include "clock.h"
@@ -69,8 +70,6 @@ class UsagePropertySet : public CdmClientPropertySet {
   const std::string empty_;
 };
 
-bool CdmEngine::seeded_ = false;
-
 CdmEngine::CdmEngine(FileSystem* file_system,
                      std::shared_ptr<metrics::EngineMetrics> metrics,
                      const std::string& spoid)
@@ -83,11 +82,7 @@ CdmEngine::CdmEngine(FileSystem* file_system,
       usage_property_set_(),
       last_usage_information_update_time_(0) {
   assert(file_system);
-  if (!seeded_) {
-    Properties::Init();
-    srand(clock_.GetCurrentTime());
-    seeded_ = true;
-  }
+  Properties::Init();
 }
 
 CdmEngine::~CdmEngine() {
@@ -1260,7 +1255,8 @@ CdmResponseType CdmEngine::GetUsageInfo(const std::string& app_id,
                                         CdmUsageInfo* usage_info) {
   LOGI("Getting usage info: app_id = %s", app_id.c_str());
   // Return a random usage report from a random security level
-  SecurityLevel security_level = ((rand() % 2) == 0) ? kLevelDefault : kLevel3;
+  SecurityLevel security_level =
+      CdmRandom::RandomBool() ? kLevelDefault : kLevel3;
   CdmResponseType status = UNKNOWN_ERROR;
   if (!usage_info) {
     LOGE("No usage info destination");
@@ -1328,7 +1324,7 @@ CdmResponseType CdmEngine::GetUsageInfo(const std::string& app_id,
 
   usage_info->resize(kUsageReportsPerRequest);
 
-  size_t index = rand() % usage_data.size();
+  size_t index = CdmRandom::RandomInRange(usage_data.size() - 1);
   status = usage_session_->RestoreUsageSession(usage_data[index], error_detail);
   if (KEY_ADDED != status) {
     LOGE("RestoreUsageSession failed: index = %zu, status = %d", index,