[Android] Add gyp support for multidex.

build/java_apk.gypi

Index: build/java_apk.gypi
diff --git a/build/java_apk.gypi b/build/java_apk.gypi
index a1fc8574db67ca4e21145a2d2205ae5c263f8ba4..a446755b29d8627c570b39afac7ecc0e6ad81212 100644
--- a/build/java_apk.gypi
+++ b/build/java_apk.gypi
@@ -131,7 +131,7 @@
     'jar_path': '<(PRODUCT_DIR)/lib.java/<(jar_name)',
     'obfuscated_jar_path': '<(intermediate_dir)/obfuscated.jar',
     'test_jar_path': '<(PRODUCT_DIR)/test.lib.java/<(apk_name).jar',
-    'dex_path': '<(intermediate_dir)/classes.dex',
+    'enable_multidex%': 0,
     'emma_device_jar': '<(android_sdk_root)/tools/lib/emma_device.jar',
     'android_manifest_path%': '<(java_in_dir)/AndroidManifest.xml',
     'split_android_manifest_path': '<(intermediate_dir)/split-manifests/<(android_app_abi)/AndroidManifest.xml',
@@ -160,6 +160,7 @@
         'unsigned_apk_path': '<(intermediate_dir)/<(apk_name)-unsigned.apk',
         'unsigned_abi_split_apk_path': '<(intermediate_dir)/<(apk_name)-abi-<(android_app_abi)-unsigned.apk',
         'create_abi_split%': 0,
+        'enable_multidex%': 0,
       },
       'unsigned_apk_path': '<(unsigned_apk_path)',
       'unsigned_abi_split_apk_path': '<(unsigned_abi_split_apk_path)',
@@ -193,6 +194,11 @@
         }, {
           'managed_input_apk_path': '<(unsigned_apk_path)',
         }],
+        ['enable_multidex == 1', {
+          'dex_path': '<(intermediate_dir)/classes.dex.zip',
+        }, {
+          'dex_path': '<(intermediate_dir)/classes.dex',
+        }],
       ],
     },
     'native_lib_target%': '',
@@ -213,6 +219,7 @@
     'native_lib_placeholder_stamp': '<(apk_package_native_libs_dir)/<(android_app_abi)/native_lib_placeholder.stamp',
     'native_lib_placeholders': [],
     'main_apk_name': '<(apk_name)',
+    'dex_path': '<(dex_path)',
     'enable_errorprone%': '0',
     'errorprone_exe_path': '<(PRODUCT_DIR)/bin.java/chromium_errorprone',
   },
@@ -993,13 +1000,36 @@
     {
       'action_name': 'dex_<(_target_name)',
       'variables': {
+        'dex_additional_options': [],
         'dex_input_paths': [
-          '>@(library_dexed_jars_paths)',
           '<(jar_path)',
         ],
         'output_path': '<(dex_path)',
         'proguard_enabled_input_path': '<(obfuscated_jar_path)',
       },
+      'conditions': [
+        ['enable_multidex == 1', {
+          'variables': {
+            'main_dex_rules_file': '<(DEPTH)/build/android/main_dex_classes.flags',
+            'dex_additional_options': [
+              '--multi-dex',
+              '--main-dex-rules-file', '<(main_dex_rules_file)',
+            ],
+            'dex_input_paths': [
+              '>@(input_jars_paths)',
+            ],
+          },
+          'inputs': [
+            '<(main_dex_rules_file)',
+          ],
+        }, {
+          'variables': {
+            'dex_input_paths': [
+              '>@(library_dexed_jars_paths)',
+            ],
+          },
+        }]
+      ],
       'target_conditions': [
         ['emma_instrument != 0', {
           'variables': {