Per-host V8 histograms.

content/renderer/render_view_impl.cc

Index: content/renderer/render_view_impl.cc
diff --git a/content/renderer/render_view_impl.cc b/content/renderer/render_view_impl.cc
index 3c1526682498c7356cdf5601f31cba94d9534be8..8f5089c793b20406e58a68631f57030e2e926d65 100644
--- a/content/renderer/render_view_impl.cc
+++ b/content/renderer/render_view_impl.cc
@@ -1118,6 +1118,17 @@ void RenderViewImpl::OnNavigate(const ViewMsg_Navigate_Params& params) {
 
   // In case LoadRequest failed before DidCreateDataSource was called.
   pending_navigation_params_.reset();
+
+  // Check if all RenderViewImpls are displaying a page from the same host, and
+  // update RenderThreadImpl's view on that. If this is the only RenderViewImpl,
+  // the common host is this view's host. If there are many, check if this one
+  // shares the common host of the other RenderViewImpls. It's ok to not detect
+  // some cases where the RenderViewImpls share a common host.

[Charlie Reis, 2012/08/16 16:22:56]

This isn't safe.  You'll miss renderer-initiated navigations (e.g., link clicks,
frame navigations, etc), and it'll often be wrong due to redirects and
downloads.  It's much safer to watch commits instead.

[marja, 2012/08/21 15:21:15]

Changed this to do the work in RenderViewImpl::didCommitProvisionalLoad. It only
tracks top frame navigations, and ignores subframes. We only take the top frame
host into account when deciding whether to produce a custom diagram since the
subframes are considered to be a part of the page.

+  RenderThreadImpl* render_thread_impl = RenderThreadImpl::current();
+  if (g_view_map.Get().size() == 1)
+    render_thread_impl->SetCommonHost(params.url.host());
+  else if (params.url.host() != render_thread_impl->CommonHost())
+    render_thread_impl->SetCommonHost(std::string());
 }
 
 bool RenderViewImpl::IsBackForwardToStaleEntry(