Use ElapsedTimer in Document instead of doubles

Document stores a timestamp for the moment it was created in order to compute
the elapsed time whenever required. This looks like the perfect use case for
base::ElapsedTimer. We wouldn't have to convert from double to int anymore.

Actually we can go further and completely get rid of int downcasts as well and
operate always in terms of base::TimeDelta. Document::ElapsedTime() returns a
base::TimeDelta from now on and it was also moved to the private section as it
isn't used from the outside.

Bug: 979137
Change-Id: I2a3ede41fa947c400769ad21c515eefb857b7fbe
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1679755Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Commit-Queue: Sergio Villar <svillar@igalia.com>
Cr-Commit-Position: refs/heads/master@{#676947}

third_party/blink/renderer/core/dom/document.cc

@@ -392,7 +392,8 @@ static const unsigned kCMaxWriteRecursionDepth = 21;
 // a layout without a delay.
 // FIXME: For faster machines this value can really be lowered to 200.  250 is
 // adequate, but a little high for dual G5s. :)
-static const int kCLayoutScheduleThreshold = 250;
+static const base::TimeDelta kCLayoutScheduleThreshold =
+    base::TimeDelta::FromMilliseconds(250);
 
 // DOM Level 2 says (letters added):
 //
@@ -989,7 +990,6 @@ Document::Document(const DocumentInit& initializer,
       was_discarded_(false),
       load_event_progress_(kLoadEventCompleted),
       is_freezing_in_progress_(false),
-      start_time_(CurrentTime()),
       script_runner_(MakeGarbageCollected<ScriptRunner>(this)),
       xml_version_("1.0"),
       xml_standalone_(kStandaloneUnspecified),
@@ -3804,7 +3804,7 @@ void Document::ImplicitClose() {
   }
 
   if (GetFrame()->Loader().HasProvisionalNavigation() &&
-      ElapsedTime() < kCLayoutScheduleThreshold) {
+      start_time_.Elapsed() < kCLayoutScheduleThreshold) {
     // Just bail out. Before or during the onload we were shifted to another
     // page.  The old i-Bench suite does this. When this happens don't bother
     // painting or laying out.
@@ -4174,10 +4174,6 @@ bool Document::ShouldScheduleLayout() const {
   return false;
 }
 
-int Document::ElapsedTime() const {
-  return static_cast<int>((CurrentTime() - start_time_) * 1000);
-}
-
 void Document::write(const String& text,
                      Document* entered_document,
                      ExceptionState& exception_state) {

third_party/blink/renderer/core/dom/document.h

@@ -772,7 +772,6 @@ class CORE_EXPORT Document : public ContainerNode,
   bool HasFinishedParsing() const { return parsing_state_ == kFinishedParsing; }
 
   bool ShouldScheduleLayout() const;
-  int ElapsedTime() const;
 
   TextLinkColors& GetTextLinkColors() { return text_link_colors_; }
   const TextLinkColors& GetTextLinkColors() const { return text_link_colors_; }
@@ -1878,7 +1877,7 @@ class CORE_EXPORT Document : public ContainerNode,
 
   bool is_freezing_in_progress_;
 
-  double start_time_;
+  base::ElapsedTimer start_time_;
 
   Member<ScriptRunner> script_runner_;