Media element: avoid v8 allocations in hasPendingActivity().

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

Index: third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
diff --git a/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp b/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
index c812addeafe4fcdf05b0df3990075b6e0e1ce6d5..1e035b6610f7b7a8f55b940cf34037239c340486 100644
--- a/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLMediaElement.cpp
@@ -283,6 +283,22 @@ String preloadTypeToString(WebMediaPlayer::Preload preloadType) {
   return String();
 }
 
+class DisablePlaybackPositionUpdateScope {
+  STACK_ALLOCATED();
+
+ public:
+  DisablePlaybackPositionUpdateScope(bool* flag)
+      : m_flag(flag), m_value(*flag) {
+    *m_flag = false;
+  }
+
+  ~DisablePlaybackPositionUpdateScope() { *m_flag = m_value; }
+
+ private:
+  bool* m_flag;
+  bool m_value;
+};
+
 }  // anonymous namespace
 
 class HTMLMediaElement::AutoplayHelperClientImpl
@@ -3458,9 +3474,17 @@ bool HTMLMediaElement::hasPendingActivity() const {
   if (m_networkState == kNetworkLoading)
     return true;
 
-  // When playing or if playback may continue, timeupdate events may be fired.
-  if (couldPlayIfEnoughData())
-    return true;
+  {
+    // Disable potential updating of playback position, as that will
+    // require v8 allocations; not allowed while GCing
+    // (hasPendingActivity() is called during a v8 GC.)
+    DisablePlaybackPositionUpdateScope scope(

[haraken, 2016/11/16 06:47:26]

Can we use  AutoReset?

[sof, 2016/11/16 08:11:16]

Thanks, I'd forgotten about TemporaryChange<> / AutoReset<> being available.

+        &m_officialPlaybackPositionNeedsUpdate);
+
+    // When playing or if playback may continue, timeupdate events may be fired.
+    if (couldPlayIfEnoughData())
+      return true;
+  }
 
   // When the seek finishes timeupdate and seeked events will be fired.
   if (m_seeking)