Move navigation and frame tree classes to a new frame_host/ directory.

content/browser/renderer_host/DEPS

 include_rules = [
   "+cc/switches.h", # For cc command line switches.
   "+media/base",  # For media command line switches.
   "+media/audio/audio_util.h",  # For audio hardware sample-rate.
   "+third_party/zlib",
   "+third_party/libyuv",
 
   # The renderer_host files should only call upwards in the layering via the
   # delegate interfaces.
+  "-content/browser/frame_host",
   "-content/browser/web_contents",
   "-content/public/browser/web_contents.h",
   "-content/public/browser/web_contents_delegate.h",
   "-content/public/browser/web_contents_view.h",
 ]
 
 specific_include_rules = {
   ".*_(unit|browser)test\.cc": [
+    "+content/browser/frame_host",
     "+content/browser/web_contents",
     "+content/public/browser/web_contents.h",
     "+content/public/browser/web_contents_view.h",
     "+media/filters",
   ],
   "render_sandbox_host_linux\.cc": [
     "+third_party/WebKit/public/web/WebKit.h",
     "+third_party/WebKit/public/web/linux/WebFontInfo.h",
   ],
+  "render_process_host_impl\.cc": [
+    "+content/browser/frame_host/render_frame_message_filter.h",
+  ],
+  # TODO(nasko): Remove these exceptions once we've untangled the dependency
+  # of RenderViewHost on the FrameTree.
+  "render_view_host_impl\.(cc|h)": [
+    "+content/browser/frame_host/frame_tree.h",
+    "+content/browser/frame_host/render_frame_host_impl.h",
+  ],
 }