Add UMAs about Blink GC metrics

Source/platform/heap/Heap.cpp

Index: Source/platform/heap/Heap.cpp
diff --git a/Source/platform/heap/Heap.cpp b/Source/platform/heap/Heap.cpp
index e353c609c3997c679011fc392b577ff1d2ea9311..b5ebff3bc99fe476babed99ab71988174ab57ecf 100644
--- a/Source/platform/heap/Heap.cpp
+++ b/Source/platform/heap/Heap.cpp
@@ -33,6 +33,7 @@
 
 #include "platform/TraceEvent.h"
 #include "platform/heap/ThreadState.h"
+#include "public/platform/Platform.h"
 #include "wtf/Assertions.h"
 #include "wtf/LeakAnnotations.h"
 #include "wtf/PassOwnPtr.h"
@@ -1648,6 +1649,7 @@ void Heap::collectGarbage(ThreadState::StackState stackState)
 
     TRACE_EVENT0("Blink", "Heap::collectGarbage");
     TRACE_EVENT_SCOPED_SAMPLING_STATE("Blink", "BlinkGC");
+    double timeStamp = WTF::currentTimeMS();
 #if ENABLE(GC_TRACING)
     static_cast<MarkingVisitor*>(s_markingVisitor)->objectGraph().clear();
 #endif
@@ -1674,6 +1676,11 @@ void Heap::collectGarbage(ThreadState::StackState stackState)
 #if ENABLE(GC_TRACING)
     static_cast<MarkingVisitor*>(s_markingVisitor)->reportStats();
 #endif
+
+    if (blink::Platform::current()) {
+        blink::Platform::current()->histogramEnumeration("BlinkGC.CollectGarbage", WTF::currentTimeMS() - timeStamp, 30000);
+        blink::Platform::current()->histogramEnumeration("BlinkGC.TotalObjectSpaceInAllThreads", totalObjectSpaceInAllThreads() / 1024, 8 * 1024 * 1024);
+    }
 }
 
 void Heap::collectAllGarbage()
@@ -1692,6 +1699,18 @@ void Heap::setForcePreciseGCForTesting()
     ThreadState::current()->setForcePreciseGCForTesting(true);
 }
 
+uint64_t Heap::totalObjectSpaceInAllThreads()

[Mads Ager (chromium), 2014/05/28 09:35:45]

Let do totalAllocatedSpaceInAllThreads and report that to UMA as well? That will
be very helpful to figure out how much fragmentation we have. If we have a very
small amount of totalObjectSpace and a much, much larger value for
totalAllocatedSpace we have a lot of fragmentation.

[haraken, 2014/05/28 10:40:26]

Done.

+{
+    uint64_t count = 0;
+    ASSERT(ThreadState::isAnyThreadInGC());
+    ThreadState::AttachedThreadStateSet& threads = ThreadState::attachedThreads();
+    typedef ThreadState::AttachedThreadStateSet::iterator ThreadStateIterator;
+    for (ThreadStateIterator it = threads.begin(), end = threads.end(); it != end; ++it) {
+        count += (*it)->stats().totalObjectSpace();
+    }
+    return count;
+}
+
 void Heap::getStats(HeapStats* stats)
 {
     stats->clear();