Android: Fix dexing a prebuilt that exceeds dex limit

There was an assumption that a single prebuilt would not have more than
64k methods, but the assumption was wrong.

Bug: None
Change-Id: I4a94c383fa47ffd7f6034e094e495e98afe70c68
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2027893
Commit-Queue: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Sky Malice <skym@chromium.org>
Reviewed-by: Sam Maier <smaier@chromium.org>
Cr-Commit-Position: refs/heads/master@{#736561}

build/android/gyp/dex.py

@@ -273,9 +273,15 @@ def _CreateFinalDex(d8_inputs, output, tmp_dir, dex_cmd, options=None):
   tmp_dex_output = os.path.join(tmp_dir, 'tmp_dex_output.zip')
   if (output.endswith('.dex')
       or not all(f.endswith('.dex') for f in d8_inputs)):
-    if options and options.main_dex_list_path:
-      # Provides a list of classes that should be included in the main dex file.
-      dex_cmd = dex_cmd + ['--main-dex-list', options.main_dex_list_path]
+    if options:
+      if options.main_dex_list_path:
+        dex_cmd = dex_cmd + ['--main-dex-list', options.main_dex_list_path]
+      elif options.multi_dex and int(options.min_api or 1) < 21:
+        # When dexing library targets, it doesn't matter what's in the main dex.
+        tmp_main_dex_list_path = os.path.join(tmp_dir, 'main_list.txt')
+        with open(tmp_main_dex_list_path, 'w') as f:
+          f.write('Foo.class\n')
+        dex_cmd = dex_cmd + ['--main-dex-list', tmp_main_dex_list_path]
 
     tmp_dex_dir = os.path.join(tmp_dir, 'tmp_dex_dir')
     os.mkdir(tmp_dex_dir)

build/config/android/internal_rules.gni

@@ -1349,6 +1349,9 @@ if (enable_java_templates) {
             deps += [ ":${_main_dex_list_target_name}" ]
             inputs += [ _main_dex_list_path ]
           }
+        } else if (defined(invoker.enable_library_multidex) &&
+                   invoker.enable_library_multidex) {
+          args += [ "--multi-dex" ]
         }
 
         if (defined(invoker.input_dex_filearg)) {
@@ -3400,9 +3403,10 @@ if (enable_java_templates) {
             output = _dex_path
             deps = [ ":$_process_prebuilt_target_name" ]
 
-            # Should never need multidex when compiling individual libraries.
-            # Disabling multidex saves on having to create a main_dex_list.
+            # For library targets, we do not need a proper main dex list, but do
+            # need to allow multiple dex files.
             enable_multidex = false
+            enable_library_multidex = true
           }
           _accumulated_public_deps += [ ":${target_name}__dex" ]
         }