Media Capabilities: rename mediacapabilities module to media_capabilities.

third_party/WebKit/Source/modules/media_capabilities/BUILD.gn

 # Copyright 2017 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.
 
 import("//third_party/WebKit/Source/modules/modules.gni")
 
-blink_modules_sources("mediacapabilities") {
+blink_modules_sources("media_capabilities") {
   sources = [
     "MediaCapabilities.cpp",
     "MediaCapabilities.h",
     "MediaDecodingAbility.cpp",
     "MediaDecodingAbility.h",
     "NavigatorMediaCapabilities.cpp",
     "NavigatorMediaCapabilities.h",
   ]
 }