Move creation and ownership of ResourceDispatcherHost and PluginService to content. This gives a few benefits:
-avoid having each embedder know when to create/destruct these objects, as well as contained objects (i.e. those related to downloads)
-avoid having to tell embedders about specifics of BrowserThread startup/shutdown
-move ResourceDispatcherHost's getter to content where it belongs

I've taken out the DnsParallelism field trial (not used anymore, confirmed with jar) as it was the only thing that caused MetricsService to depend on IOThread initialization, which also depended on MetricsService (through FieldTrials). This two-sided dependency always annoyed me and made the code hard to restructure.

BUG=98716
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=117078
Review URL: http://codereview.chromium.org/9150016

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@117171 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/content/shell/shell_content_browser_client.cc b/content/shell/shell_content_browser_client.cc
index 73e8a5cc..904e9ff 100644
--- a/content/shell/shell_content_browser_client.cc
+++ b/content/shell/shell_content_browser_client.cc
@@ -245,8 +245,7 @@
   return std::string();
 }
 
-ResourceDispatcherHost* ShellContentBrowserClient::GetResourceDispatcherHost() {
-  return shell_browser_main_parts_->GetResourceDispatcherHost();
+void ShellContentBrowserClient::ResourceDispatcherHostCreated() {
 }
 
 ui::Clipboard* ShellContentBrowserClient::GetClipboard() {