Pass ownership of the kernel bytes to the Dart_LoadKernel. (#4078)

This is follow-up to https://github.com/dart-lang/sdk/commit/c7faf2dc6b64b65e04d677fa3ad68c1e90e19bff, which made Dart_LoadKernel responsible for the bytes.

runtime/dart_controller.cc

@@ -45,7 +45,7 @@ std::string ResolvePath(std::string path) {
 }  // namespace
 
 DartController::DartController() : ui_dart_state_(nullptr),
-    kernel_bytes(nullptr), platform_kernel_bytes(nullptr) {}
+    platform_kernel_bytes(nullptr) {}
 
 DartController::~DartController() {
   if (ui_dart_state_) {
@@ -56,9 +56,6 @@ DartController::~DartController() {
     Dart_ShutdownIsolate();  // deletes ui_dart_state_
     ui_dart_state_ = nullptr;
   }
-  if (kernel_bytes) {
-    free(kernel_bytes);
-  }
   if (platform_kernel_bytes) {
     free(platform_kernel_bytes);
   }
@@ -113,9 +110,9 @@ static void CopyVectorBytes(const std::vector<uint8_t>& vector,
 tonic::DartErrorHandleType DartController::RunFromKernel(
     const std::vector<uint8_t>& kernel) {
   tonic::DartState::Scope scope(dart_state());
-  // Copy kernel bytes so they won't go away after we exit this method.
-  // This is needed because original kernel data has to be available
-  // during code execution.
+  // Copy kernel bytes and pass ownership of the copy to the Dart_LoadKernel,
+  // which is expected to release them.
+  uint8_t* kernel_bytes = nullptr;
   CopyVectorBytes(kernel, kernel_bytes);
 
   Dart_Handle result = Dart_LoadKernel(

runtime/dart_controller.h

@@ -42,10 +42,6 @@ class DartController {
   // during isolate shutdown.
   UIDartState* ui_dart_state_;
 
-  // Kernel binary image of dart script. This is copied and maintained
-  // for dart script lifespan, so that kernel loading mechanism can
-  // incrementally build the dart objects from it.
-  uint8_t* kernel_bytes;
   // Kernel binary image of platform core libraries. This is copied and
   // maintained for dart script lifespan, so that kernel loading mechanism can
   // incrementally build the dart objects from it.