Fix a startup performance issue with the ModuleDatabase feature

The ModuleEventSink interface was bound on the UI thread, which caused
cross-process IPC to retrieve information about a loaded module in the
renderer process.

A new sequence with background priority is instead used so that it
doesn't impact startup.

Bug: 832286
Change-Id: I5ab50bc45386c9a1ddb2888f80293d78bd768a88
Reviewed-on: https://chromium-review.googlesource.com/1037935Reviewed-by: Chris Hamilton <chrisha@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Patrick Monette <pmonette@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558010}

chrome/browser/chrome_browser_main_win.cc

@@ -345,7 +345,7 @@ void OnModuleEvent(const ModuleWatcher::ModuleEvent& event) {
         // task.
         base::PostTaskWithTraits(
             FROM_HERE,
-            {base::MayBlock(),
+            {base::MayBlock(), base::TaskPriority::BACKGROUND,
              base::TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN},
             base::Bind(&HandleModuleLoadEventWithoutTimeDateStamp,
                        event.module_path, event.module_size, load_address));

chrome/browser/chrome_content_browser_client.cc

@@ -28,6 +28,7 @@
 #include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/sys_info.h"
+#include "base/task_scheduler/post_task.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "build/build_config.h"
 #include "chrome/browser/after_startup_task_utils.h"
@@ -3276,9 +3277,8 @@ void ChromeContentBrowserClient::ExposeInterfacesToRenderer(
     // process handle is not yet available at this point so pass in a callback
     // to allow it to be retrieved at the time the interface is actually
     // created. It is safe to pass a raw pointer to |render_process_host|: the
-    // callback will be invoked in the context of ModuleDatabase::GetInstance,
-    // which is invoked by Mojo initialization, which occurs while the
-    // |render_process_host| is alive.
+    // callback will be invoked in the context of Mojo initialization, which
+    // occurs while the |render_process_host| is alive.
     auto get_process = base::BindRepeating(
         [](content::RenderProcessHost* host) -> base::ProcessHandle {
           return host->GetProcess().Handle();
@@ -3291,7 +3291,9 @@ void ChromeContentBrowserClient::ExposeInterfacesToRenderer(
                             std::move(get_process),
                             content::PROCESS_TYPE_RENDERER,
                             base::Unretained(ModuleDatabase::GetInstance())),
-        ui_task_runner);
+        base::CreateSequencedTaskRunnerWithTraits(
+            {base::TaskPriority::BACKGROUND,
+             base::TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN}));
   }
 #endif
 

chrome/browser/conflicts/module_event_sink_impl_win.cc

@@ -8,6 +8,7 @@
 
 #include <psapi.h>
 
+#include <memory>
 #include <utility>
 #include <vector>
 
@@ -111,7 +112,6 @@ void ModuleEventSinkImpl::Create(
     content::ProcessType process_type,
     ModuleDatabase* module_database,
     mojom::ModuleEventSinkRequest request) {
-  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
   base::ProcessHandle process = get_process_handle.Run();
   auto module_event_sink_impl = std::make_unique<ModuleEventSinkImpl>(
       process, process_type, module_database);