Update uses of UTF conversions in content/ to use the base:: namespace.

content/browser/renderer_host/render_widget_host_view_mac_unittest.mm

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/renderer_host/render_widget_host_view_mac.h"
 
 #include "base/mac/mac_util.h"
 #include "base/mac/scoped_nsautorelease_pool.h"
 #include "base/strings/utf_string_conversions.h"
 #include "content/browser/browser_thread_impl.h"
@@ skipping 306 matching lines @@
   // Command-ESC will destroy the view, while the window is still in
   // |-performKeyEquivalent:|.  There are other cases where this can
   // happen, Command-ESC is the easiest to trigger.
   [[view->cocoa_view() window] performKeyEquivalent:
       cocoa_test_event_utils::KeyEventWithKeyCode(
           53, 27, NSKeyDown, NSCommandKeyMask)];
   observer.Wait();
 }
 
 TEST_F(RenderWidgetHostViewMacTest, GetFirstRectForCharacterRangeCaretCase) {
-  const base::string16 kDummyString = UTF8ToUTF16("hogehoge");
+  const base::string16 kDummyString = base::UTF8ToUTF16("hogehoge");
   const size_t kDummyOffset = 0;
 
   gfx::Rect caret_rect(10, 11, 0, 10);
   gfx::Range caret_range(0, 0);
   ViewHostMsg_SelectionBounds_Params params;
 
   NSRect rect;
   NSRange actual_range;
   rwhv_mac_->SelectionChanged(kDummyString, kDummyOffset, caret_range);
   params.anchor_rect = params.focus_rect = caret_rect;
@@ skipping 444 matching lines @@
   host->OnMessageReceived(*response2);
 
   // Check that the view delegate ignored the empty unhandled wheel event.
   ASSERT_EQ(NO, view_delegate.get().unhandledWheelEventReceived);
 
   // Clean up.
   host->Shutdown();
 }
 
 }  // namespace content