v8binding: Fix the return types of MemoryInfo APIs

Fixes the return types in C++ accodring to the ones in Web IDL.
|unsigned long long| in Web IDL corresponds to |uint64_t| in C++.

Change-Id: I43ab122bb94fc066f7b2de39b66c2ee08496de37
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2148915Reviewed-by: Hitoshi Yoshida <peria@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Yuki Shiino <yukishiino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#759166}

third_party/blink/renderer/core/timing/memory_info.h

@@ -62,9 +62,9 @@ class CORE_EXPORT MemoryInfo final : public ScriptWrappable {
 
   explicit MemoryInfo(Precision precision);
 
-  size_t totalJSHeapSize() const { return info_.total_js_heap_size; }
-  size_t usedJSHeapSize() const { return info_.used_js_heap_size; }
-  size_t jsHeapSizeLimit() const { return info_.js_heap_size_limit; }
+  uint64_t totalJSHeapSize() const { return info_.total_js_heap_size; }
+  uint64_t usedJSHeapSize() const { return info_.used_js_heap_size; }
+  uint64_t jsHeapSizeLimit() const { return info_.js_heap_size_limit; }
 
  private:
   FRIEND_TEST_ALL_PREFIXES(MemoryInfoTest, Bucketized);