Avoid unnecessary DocumentElementSetMap hash table updates.

third_party/WebKit/Source/core/html/HTMLMediaElement.cpp

 /*
  * Copyright (C) 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 89 matching lines @@
 // Default to not logging warnings about excessive drift in the cached media time because it adds a
 // fair amount of overhead and logging.
 #define LOG_CACHED_TIME_WARNINGS 0
 #endif
 
 namespace blink {
 
 using namespace HTMLNames;
 
 using WeakMediaElementSet = HeapHashSet<WeakMember<HTMLMediaElement>>;
-using DocumentElementSetMap = HeapHashMap<WeakMember<Document>, WeakMediaElementSet>;
+using DocumentElementSetMap = HeapHashMap<WeakMember<Document>, Member<WeakMediaElementSet>>;
 
 namespace {
 
 // URL protocol used to signal that the media source API is being used.
 const char mediaSourceBlobProtocol[] = "blob";
 
 enum MediaControlsShow {
     MediaControlsShowAttribute = 0,
     MediaControlsShowFullscreen,
     MediaControlsShowNoScript,
@@ skipping 19 matching lines @@
 
 DocumentElementSetMap& documentToElementSetMap()
 {
     DEFINE_STATIC_LOCAL(DocumentElementSetMap, map, (new DocumentElementSetMap));
     return map;
 }
 
 void addElementToDocumentMap(HTMLMediaElement* element, Document* document)
 {
     DocumentElementSetMap& map = documentToElementSetMap();
-    WeakMediaElementSet set = map.take(document);
-    set.add(element);
-    map.add(document, set);
+    WeakMediaElementSet* set = nullptr;
+    auto it = map.find(document);
+    if (it == map.end()) {
+        set = new WeakMediaElementSet;
+        map.add(document, set);
+    } else {
+        set = it->value;
+    }
+    set->add(element);
 }
 
 void removeElementFromDocumentMap(HTMLMediaElement* element, Document* document)
 {
     DocumentElementSetMap& map = documentToElementSetMap();
-    WeakMediaElementSet set = map.take(document);
-    set.remove(element);
-    if (!set.isEmpty())
-        map.add(document, set);
+    auto it = map.find(document);
+    ASSERT(it != map.end());
+    WeakMediaElementSet* set = it->value;
+    set->remove(element);
+    if (set->isEmpty())
+        map.remove(it);
 }
 
 class AudioSourceProviderClientLockScope {
     STACK_ALLOCATED();
 public:
     AudioSourceProviderClientLockScope(HTMLMediaElement& element)
         : m_client(element.audioSourceNode())
     {
         if (m_client)
             m_client->lock();
@@ skipping 3177 matching lines @@
     m_processingPreferenceChange = false;
 
     // As track visibility changed while m_processingPreferenceChange was set,
     // there was no call to updateTextTrackDisplay(). This call is not in the
     // spec, see the note in configureTextTrackDisplay().
     updateTextTrackDisplay();
 }
 
 void HTMLMediaElement::setTextTrackKindUserPreferenceForAllMediaElements(Document* document)
 {
-    WeakMediaElementSet elements = documentToElementSetMap().get(document);
+    auto it = documentToElementSetMap().find(document);
+    if (it == documentToElementSetMap().end())
+        return;
+    ASSERT(it->value);
+    WeakMediaElementSet& elements = *it->value;
     for (const auto& element : elements)
         element->automaticTrackSelectionForUpdatedUserPreference();
 }
 
 void HTMLMediaElement::automaticTrackSelectionForUpdatedUserPreference()
 {
     if (!m_textTracks || !m_textTracks->length())
         return;
 
     markCaptionAndSubtitleTracksAsUnconfigured();
@@ skipping 500 matching lines @@
 }
 
 #if !ENABLE(OILPAN)
 WeakPtr<HTMLMediaElement> HTMLMediaElement::createWeakPtr()
 {
     return m_weakPtrFactory.createWeakPtr();
 }
 #endif
 
 } // namespace blink