Remove <(webrtc_root) from source file entries.

This required to move the AGC tools source files
into webrtc/tools and create a new agc_test_utils target.

Since audio_codec_speed_tests.gypi referenced sources above,
the best approach I could come up with was to add an audio_coding.gypi
file at a higher level and move the targets in there (+ the includes from
modules.gyp which is an improvement IMO).

I also added a PRESUBMIT.py check to prevent new source
entries being added with <(webrtc_root) in the path.

BUG=4185
R=andrew@webrtc.org, tina.legrand@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/37859004

Cr-Commit-Position: refs/heads/master@{#8197}
git-svn-id: http://webrtc.googlecode.com/svn/trunk@8197 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimator.gypi

@@ -61,6 +61,7 @@
       'dependencies': [
         '<(webrtc_root)/system_wrappers/system_wrappers.gyp:system_wrappers',
         '<(webrtc_root)/system_wrappers/system_wrappers.gyp:system_wrappers_default',
+        '<(webrtc_root)/test/test.gyp:rtp_test_utils',
         'bwe_tools_util',
         'rtp_rtcp',
       ],
@@ -71,8 +72,6 @@
       },
       'sources': [
         'tools/rtp_to_text.cc',
-        '<(webrtc_root)/test/rtp_file_reader.cc',
-        '<(webrtc_root)/test/rtp_file_reader.h',
       ], # source
     },
     {
@@ -84,6 +83,7 @@
       'dependencies': [
         '<(webrtc_root)/system_wrappers/system_wrappers.gyp:system_wrappers',
         '<(webrtc_root)/system_wrappers/system_wrappers.gyp:system_wrappers_default',
+        '<(webrtc_root)/test/test.gyp:rtp_test_utils',
         'bwe_tools_util',
         'rtp_rtcp',
       ],
@@ -94,8 +94,6 @@
       },
       'sources': [
         'tools/bwe_rtp_play.cc',
-        '<(webrtc_root)/test/rtp_file_reader.cc',
-        '<(webrtc_root)/test/rtp_file_reader.h',
       ], # source
     },
   ], # targets