[Android] Rework multidex and enable multidex for unit_tests_apk.

base/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.
 
 # HOW TO WRITE CONDITIONALS IN THIS FILE
 # ======================================
 #
 # In many other places, one would write a conditional that expresses all the
 # cases when a source file is used or unused, and then either add or subtract
 # it from the sources list in that case
@@ skipping 2037 matching lines @@
       ":base_native_libraries_gen",
     ]
 
     deps = [
       "//third_party/android_tools:android_support_multidex_java",
       "//third_party/jsr-305:jsr_305_javalib",
     ]
 
     DEPRECATED_java_in_dir = "android/java/src"
 
-    # A new version of NativeLibraries.java (with the actual correct values)
-    # will be created when creating an apk.
+    # New versions of ChromiumMultiDex.java and NativeLibraries.java
+    # (with the actual correct values) will be created when creating an apk.
     jar_excluded_patterns = [
+      "*/ChromiumMultiDex.class",
       "*/NativeLibraries.class",
       "*/NativeLibraries##*.class",
     ]
   }
 
   # GYP: //base.gyp:base_javatests
   android_library("base_javatests") {
     deps = [
       ":base_java",
       ":base_java_test_support",
@@ skipping 48 matching lines @@
       "android/library_loader/library_loader_hooks.h",
       "memory/memory_pressure_listener.h",
     ]
   }
 
   # GYP: //base/base.gyp:base_multidex_gen
   java_cpp_template("base_multidex_gen") {
     sources = [
       "android/java/templates/ChromiumMultiDex.template",
     ]
-    if (is_debug) {
-      defines = [ "MULTIDEX_CONFIGURATION_Debug" ]
-    }
     package_name = "org/chromium/base/multidex"
   }
 
   # GYP: //base/base.gyp:base_native_libraries_gen
   java_cpp_template("base_native_libraries_gen") {
     sources = [
       "android/java/templates/NativeLibraries.template",
     ]
     package_name = "org/chromium/base/library_loader"
   }
 
   # GYP: //base.gyp:base_java_unittest_support
   android_library("base_java_unittest_support") {
     deps = [
       ":base_java",
     ]
     java_files =
         [ "test/android/java/src/org/chromium/base/ContentUriTestUtils.java" ]
   }
 }