Add a histogram for renderer memory usage.

content/renderer/render_thread_impl.cc

Index: content/renderer/render_thread_impl.cc
diff --git a/content/renderer/render_thread_impl.cc b/content/renderer/render_thread_impl.cc
index ce775a8f7c9126b4f77ea09f6fad079fe7c363d8..23510c9a0f4936f4d112c338f843489c4263c8a7 100644
--- a/content/renderer/render_thread_impl.cc
+++ b/content/renderer/render_thread_impl.cc
@@ -206,7 +206,9 @@ class RenderThreadImpl::GpuVDAContextLostCallback
   }
 };
 
-RenderThreadImpl::HistogramCustomizer::HistogramCustomizer() {
+RenderThreadImpl::HistogramCustomizer::HistogramCustomizer()
+    : memory_renderer_used_(NULL) {
+  custom_histograms_.insert("Memory.RendererUsed");
   custom_histograms_.insert("V8.MemoryExternalFragmentationTotal");
   custom_histograms_.insert("V8.MemoryHeapSampleTotalCommitted");
   custom_histograms_.insert("V8.MemoryHeapSampleTotalUsed");
@@ -246,9 +248,22 @@ void RenderThreadImpl::HistogramCustomizer::SetCommonHost(
     common_host_ = host;
     common_host_histogram_suffix_ = HostToCustomHistogramSuffix(host);
     v8::V8::SetCreateHistogramFunction(CreateHistogram);
+    memory_renderer_used_ = NULL;
   }
 }
 
+base::Histogram* RenderThreadImpl::HistogramCustomizer::memory_renderer_used() {
+  if (!memory_renderer_used_) {
+    memory_renderer_used_ = base::Histogram::FactoryGet(
+        ConvertToCustomHistogramName("Memory.RendererUsed"),
+        1000,
+        500000,
+        50,
+        base::Histogram::kUmaTargetedHistogramFlag);
+  }
+  return memory_renderer_used_;
+}
+
 RenderThreadImpl* RenderThreadImpl::current() {
   return lazy_tls.Pointer()->Get();
 }