Fix UMA stats for WASM function size

The code was updating the UMA stats for V8.WasmFunctionSizeBytes when
the WASM function was decoded. Unfortunately, decoding of functions is
no longer done as a separate step. Rather, it is done as part of the
compilation step.

This CL moves the UMA updates to the compilation step.

Bug: v8:7032
Change-Id: I4679036035540fabd43855c1ba5ba66ffee6762a
Reviewed-on: https://chromium-review.googlesource.com/754023
Commit-Queue: Karl Schimpf <kschimpf@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49117}

src/compiler/wasm-compiler.cc

@@ -4719,6 +4719,11 @@ WasmCompilationUnit::~WasmCompilationUnit() {
 }
 
 void WasmCompilationUnit::ExecuteCompilation() {
+  auto size_histogram = env_->module->is_wasm()
+                            ? counters()->wasm_wasm_function_size_bytes()
+                            : counters()->wasm_asm_function_size_bytes();
+  size_histogram->AddSample(
+      static_cast<int>(func_body_.end - func_body_.start));
   auto timed_histogram = env_->module->is_wasm()
                              ? counters()->wasm_compile_wasm_function_time()
                              : counters()->wasm_compile_asm_function_time();

src/wasm/module-decoder.cc

@@ -738,10 +738,6 @@ 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};