Move --user-agent overriding logic from chrome into content.

content/test/content_test_suite.cc

Index: content/test/content_test_suite.cc
diff --git a/content/test/content_test_suite.cc b/content/test/content_test_suite.cc
index be090fe354e9161bde76d2921d0aa4acab8d2618..ddeb6d16b008e5bbb0005934b8ee66207b174161 100644
--- a/content/test/content_test_suite.cc
+++ b/content/test/content_test_suite.cc
@@ -31,7 +31,7 @@ class TestContentClientInitializer : public testing::EmptyTestEventListener {
 
     DCHECK(!content::GetContentClient());
     content_client_.reset(new TestContentClient);
-    content::SetContentClient(content_client_.get());
+    content::Initialize(content_client_.get(), "TestContentClient");
 
     content_browser_client_.reset(new content::MockContentBrowserClient());
     content_client_->set_browser(content_browser_client_.get());
@@ -41,7 +41,7 @@ class TestContentClientInitializer : public testing::EmptyTestEventListener {
     notification_service_.reset();
 
     DCHECK_EQ(content_client_.get(), content::GetContentClient());
-    content::SetContentClient(NULL);
+    content::Uninitialize();
     content_client_.reset();
 
     content_browser_client_.reset();
@@ -81,4 +81,3 @@ void ContentTestSuite::Initialize() {
       testing::UnitTest::GetInstance()->listeners();
   listeners.Append(new TestContentClientInitializer);
 }
-