Add the mips_dsp_rev build variable.

build/config/compiler/BUILD.gn

 # Copyright (c) 2013 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("//build/config/android/config.gni")
 if (cpu_arch == "arm") {
   import("//build/config/arm.gni")
 }
 if (cpu_arch == "mipsel" || cpu_arch == "mips64el") {
   import("//build/config/mips.gni")
@@ skipping 283 matching lines @@
           cflags += [
             "-mips32r2",
             "-Wa,-mips32r2",
           ]
         } else if (mips_arch_variant == "r1") {
           cflags += [
             "-mips32",
             "-Wa,-mips32",
           ]
         }
+
+        if (mips_dsp_rev == 1) {
+          cflags += [ "-mdsp" ]
+        } else if (mips_dsp_rev == 2) {
+          cflags += [ "-mdspr2" ]
+        }
       }
     } else if (cpu_arch == "mips64el") {
       # Don't set the compiler flags for the WebView build. These will come
       # from the Android build system.
       if (!is_android_webview_build) {
         if (mips_arch_variant == "r6") {
           cflags += [
             "-mips64r6",
             "-Wa,-mips64r6",
           ]
@@ skipping 739 matching lines @@
       cflags += [ "-gsplit-dwarf" ]
     }
   }
 }
 
 config("no_symbols") {
   if (!is_win) {
     cflags = [ "-g0" ]
   }
 }