Move process-per-site logic from BrowsingInstance to RenderProcessHost.

chrome/browser/extensions/process_management_browsertest.cc

Index: chrome/browser/extensions/process_management_browsertest.cc
diff --git a/chrome/browser/extensions/process_management_browsertest.cc b/chrome/browser/extensions/process_management_browsertest.cc
index 9eac07c0bf0903e0c745530105cc33196e2ce79a..048792cfa667e1be04efe5c86c45ceed4836055c 100644
--- a/chrome/browser/extensions/process_management_browsertest.cc
+++ b/chrome/browser/extensions/process_management_browsertest.cc
@@ -157,6 +157,8 @@ IN_PROC_BROWSER_TEST_F(ProcessManagementTest, ProcessOverflow) {
   EXPECT_NE(ntp1_host, extension1_host);
 
   // Hosted apps only share with each other.
+  // Note that hosted2_host's app has the background permission and will use
+  // process-per-site mode, but it should still share with hosted1_host's app.
   EXPECT_EQ(hosted1_host, hosted2_host);
   EXPECT_NE(hosted1_host, web1_host);
   EXPECT_NE(hosted1_host, extension1_host);