Experiment: assert for stack-allocated GarbageCollected<>s.

third_party/WebKit/Source/platform/heap/StackFrameDepth.h

Index: third_party/WebKit/Source/platform/heap/StackFrameDepth.h
diff --git a/third_party/WebKit/Source/platform/heap/StackFrameDepth.h b/third_party/WebKit/Source/platform/heap/StackFrameDepth.h
index 94379aa71692505ddc0cfdd4a82680c1f28216cf..3b12868e90aa0708962091f34507d502bc3ef465 100644
--- a/third_party/WebKit/Source/platform/heap/StackFrameDepth.h
+++ b/third_party/WebKit/Source/platform/heap/StackFrameDepth.h
@@ -51,6 +51,18 @@ public:
     }
 #endif
 
+    static bool isStackAddress(void* pointer)
+    {
+        uint8_t* address = reinterpret_cast<uint8_t*>(pointer);
+        uint8_t* stackBase = reinterpret_cast<uint8_t*>(getStackStart());
+        if (address > stackBase)
+            return false;
+        size_t stackSize = getUnderestimatedStackSize();
+        if (!stackSize)
+            return false;
+        return (address >= stackBase - stackSize);
+    }
+
     static size_t getUnderestimatedStackSize();
     static void* getStackStart();