Update audio_processing module

Corresponds to upstream commit 524e9b043e7e86fd72353b987c9d5f6a1ebf83e1

Update notes:

 * Pull in third party license file

 * Replace .gypi files with BUILD.gn to keep track of what changes
   upstream

 * Bunch of new filse pulled in as dependencies

 * Won't build yet due to changes needed on top of these

webrtc/base/Makefile.am

@@ -0,0 +1,27 @@
+noinst_LTLIBRARIES = libbase.la
+
+noinst_HEADERS = arraysize.h \
+		 basictypes.h \
+		 checks.h \
+		 constructormagic.h \
+		 safe_conversions.h \
+		 safe_conversions_impl.h \
+		 scoped_ptr.h \
+		 template_util.h \
+		 thread_annotations.h
+
+libbase_la_SOURCES = criticalsection.cc \
+		     criticalsection.h \
+		     event.cc \
+		     event.h \
+		     platform_thread.cc \
+		     platform_thread.h \
+		     platform_file.cc \
+		     platform_file.h \
+		     stringutils.cc \
+		     stringutils.h \
+		     thread_checker.h \
+		     thread_checker_impl.cc \
+		     thread_checker_impl.h
+
+libbase_la_CXXFLAGS = $(AM_CXXFLAGS) $(COMMON_CXXFLAGS)