Fix UMA stats for WASM functions

Fixes the collection of V8.WasmFuncctionSizeBytes.wasm for UMA stats.

Bug: v8:6852
Change-Id: Ib25d249dd2856ffb8a3205e54ba052c1bc9a09cf
Reviewed-on: https://chromium-review.googlesource.com/678448Reviewed-by: Mircea Trofin <mtrofin@chromium.org>
Commit-Queue: Karl Schimpf <kschimpf@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48125}

src/wasm/function-body-decoder.cc

@@ -777,11 +777,7 @@ DecodeResult VerifyWasmCodeWithStats(AccountingAllocator* allocator,
                                      const wasm::WasmModule* module,
                                      FunctionBody& body, bool is_wasm,
                                      Counters* counters) {
-  auto size_histogram = is_wasm ? counters->wasm_wasm_function_size_bytes()
-                                : counters->wasm_asm_function_size_bytes();
-  // TODO(bradnelson): Improve histogram handling of ptrdiff_t.
   CHECK_LE(0, body.end - body.start);
-  size_histogram->AddSample(static_cast<int>(body.end - body.start));
   auto time_counter = is_wasm ? counters->wasm_decode_wasm_function_time()
                               : counters->wasm_decode_asm_function_time();
   TimedHistogramScope wasm_decode_function_time_scope(time_counter);

src/wasm/module-decoder.cc

@@ -733,6 +733,10 @@ class ModuleDecoderImpl : public Decoder {
 
   void DecodeFunctionBody(uint32_t index, uint32_t length, uint32_t offset,
                           bool verify_functions) {
+    auto size_histogram = module_->is_wasm()
+                              ? GetCounters()->wasm_wasm_function_size_bytes()
+                              : GetCounters()->wasm_asm_function_size_bytes();
+    size_histogram->AddSample(length);
     WasmFunction* function =
         &module_->functions[index + module_->num_imported_functions];
     function->code = {offset, length};
@@ -1437,6 +1441,11 @@ FunctionResult DecodeWasmFunction(Isolate* isolate, Zone* zone,
   size_t size = function_end - function_start;
   if (function_start > function_end)
     return FunctionResult::Error("start > end");
+  auto size_histogram = module->is_wasm()
+                            ? counters->wasm_wasm_function_size_bytes()
+                            : counters->wasm_asm_function_size_bytes();
+  // TODO(bradnelson): Improve histogram handling of ptrdiff_t.
+  size_histogram->AddSample(static_cast<int>(size));
   if (size > kV8MaxWasmFunctionSize)
     return FunctionResult::Error("size > maximum function size: %zu", size);
   ModuleDecoderImpl decoder(function_start, function_end, kWasmOrigin);