[wasm] Fix memory size dcheck in WasmContext

Even though kSpecMaxWasmMemoryPages == WasmModule::kPageSize, the
computation {wasm::kV8MaxWasmMemoryPages *
wasm::kSpecMaxWasmMemoryPages} is semantically wrong.

R=titzer@chromium.org

Change-Id: If4a875c714f1ca3c1fc928ec79b8be8aab62e8d0
Reviewed-on: https://chromium-review.googlesource.com/850072Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50375}

src/wasm/wasm-limits.h

@@ -41,6 +41,8 @@ constexpr size_t kV8MaxWasmTables = 1;
 constexpr size_t kV8MaxWasmMemories = 1;
 
 constexpr size_t kSpecMaxWasmMemoryPages = 65536;
+static_assert(kV8MaxWasmMemoryPages <= kSpecMaxWasmMemoryPages,
+              "v8 should not be more permissive than the spec");
 constexpr size_t kSpecMaxWasmTableSize = 0xFFFFFFFFu;
 
 constexpr uint64_t kWasmMaxHeapOffset =

src/wasm/wasm-objects.h

@@ -14,6 +14,7 @@
 #include "src/wasm/decoder.h"
 #include "src/wasm/wasm-interpreter.h"
 #include "src/wasm/wasm-limits.h"
+#include "src/wasm/wasm-module.h"
 
 #include "src/heap/heap.h"
 
@@ -69,7 +70,7 @@ struct WasmContext {
 
   inline void SetRawMemory(void* mem_start, size_t mem_size) {
     DCHECK_LE(mem_size,
-              wasm::kV8MaxWasmMemoryPages * wasm::kSpecMaxWasmMemoryPages);
+              wasm::kV8MaxWasmMemoryPages * wasm::WasmModule::kPageSize);
     this->mem_start = static_cast<byte*>(mem_start);
     this->mem_size = static_cast<uint32_t>(mem_size);
     this->mem_mask = base::bits::RoundUpToPowerOfTwo32(this->mem_size) - 1;