[vm] Globally intercept new (zone) DoesNotExtendZoneAllocated().

Cf. 479430235c

TEST=ci
Change-Id: Ice55e5083096591b1c7e1243a12ea4aa160efb0b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/209740
Commit-Queue: Ryan Macnak <rmacnak@google.com>
Reviewed-by: Slava Egorov <vegorov@google.com>

runtime/vm/allocation.h

@@ -75,4 +75,8 @@ class ZoneAllocated {
 
 }  // namespace dart
 
+// Prevent use of `new (zone) DoesNotExtendZoneAllocated()`, which places the
+// DoesNotExtendZoneAllocated on top of the Zone.
+void* operator new(size_t size, dart::Zone* zone) = delete;
+
 #endif  // RUNTIME_VM_ALLOCATION_H_

runtime/vm/zone.cc

@@ -163,8 +163,7 @@ void Zone::Segment::DecrementMemoryCapacity(uintptr_t size) {
 // is created within a new thread or ApiNativeScope when calculating high
 // watermarks or memory consumption.
 Zone::Zone()
-    : canary_(kCanary),
-      position_(reinterpret_cast<uword>(&buffer_)),
+    : position_(reinterpret_cast<uword>(&buffer_)),
       limit_(position_ + kInitialChunkSize),
       head_(NULL),
       large_segments_(NULL),
@@ -179,7 +178,6 @@ Zone::Zone()
 }
 
 Zone::~Zone() {
-  ASSERT(canary_ == kCanary);
   if (FLAG_trace_zones) {
     DumpZoneSizes();
   }

runtime/vm/zone.h

@@ -141,10 +141,6 @@ class Zone {
   template <class ElementType>
   static inline void CheckLength(intptr_t len);
 
-  // Guard against `new (zone) DoesNotExtendZoneAllocated()`.
-  static constexpr uint64_t kCanary = 0x656e6f7a74726164ull;  // "dartzone"
-  uint64_t canary_;
-
   // The free region in the current (head) segment or the initial buffer is
   // represented as the half-open interval [position, limit). The 'position'
   // variable is guaranteed to be aligned as dictated by kAlignment.