Reland "Android: Increase default_min_sdk_version 19 -> 21"

This reverts commit a71864a7.

Reason for revert:
 * Added min_sdk_version to cronet targets
 * Made dex.py not package incremental dex in cronet's test apks

Original change's description:
> Revert "Android: Increase default_min_sdk_version 19 -> 21"
>
> This reverts commit ce14e58b.
>
> Reason for revert: The CL causes failures on Cronet KitKat builders https://ci.chromium.org/p/chromium/builders/ci/android-cronet-kitkat-arm-rel
>
> The error code is INSTALL_FAILED_OLDER_SDK
> https://logs.chromium.org/logs/chromium/buildbucket/cr-buildbucket.appspot.com/8878029920810653312/+/steps/cronet_smoketests_missing_native_library_instrumentation_apk_on_Android_device_Nexus_5/0/stdout
>
> Original change's description:
> > Android: Increase default_min_sdk_version 19 -> 21
> >
> > Cronet is the only project that requires a lower minSdkVersion. To
> > continue supporting building of their targets, this change enabled
> > proguard on all of their apks in order to have all files desugared at
> > the proper minApiVersion.
> >
> > This change should speed up compiles somewhat, as it removes the need to
> > generate main-dex-lists for legacy multidex purposes.
> >
> > Bug: 1091919
> > Change-Id: Ifd8089bbf4965b55a13dea11464ccda979fd5028
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2233581
> > Reviewed-by: Peter Wen <wnwen@chromium.org>
> > Commit-Queue: Andrew Grieve <agrieve@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#776166}
>
> TBR=wnwen@chromium.org,agrieve@chromium.org
>
> Change-Id: Id4b92d5549d13de9684f542ce646993c3833795f
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: 1091919
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2236715
> Reviewed-by: Pavel Yatsuk <pavely@chromium.org>
> Commit-Queue: Pavel Yatsuk <pavely@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#776237}

Bug: 1091919
Change-Id: Ie2dc5d64739a3f57c36f3380502d290129d634f2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2235737
Commit-Queue: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Peter Wen <wnwen@chromium.org>
Reviewed-by: Paul Jensen <pauljensen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#776952}

build/android/gyp/dex.py

@@ -62,6 +62,9 @@ def _ParseArgs(args):
       '--multi-dex',
       action='store_true',
       help='Allow multiple dex files within output.')
+  parser.add_argument('--library',
+                      action='store_true',
+                      help='Allow numerous dex files within output.')
   parser.add_argument('--r8-jar-path', required=True, help='Path to R8 jar.')
   parser.add_argument('--desugar', action='store_true')
   parser.add_argument(
@@ -334,13 +337,15 @@ def _PerformDexlayout(tmp_dir, tmp_dex_output, options):
 
 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)):
+  needs_dexing = not all(f.endswith('.dex') for f in d8_inputs)
+  needs_dexmerge = output.endswith('.dex') or not (options and options.library)
+  if needs_dexing or needs_dexmerge:
     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.
+      elif options.library and int(options.min_api or 1) < 21:
+        # When dexing D8 requires a main dex list pre-21. For library targets,
+        # it doesn't matter what's in the main dex, so just use a dummy one.
         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')

build/config/android/config.gni

@@ -46,9 +46,8 @@ if (is_android || is_chromeos) {
     enable_chrome_android_internal = has_chrome_android_internal
 
     # The default to use for android:minSdkVersion for targets that do
-    # not explicitly set it. This can generally be set higher than the
-    # default, but not lower.
-    default_min_sdk_version = 19
+    # not explicitly set it.
+    default_min_sdk_version = 21
 
     # Android API level for 32 bits platforms
     android32_ndk_api_level = 16

build/config/android/internal_rules.gni

@@ -1304,6 +1304,9 @@ if (enable_java_templates) {
       }
     }
 
+    # It's not safe to dex merge with libraries dex'ed at higher api versions.
+    assert(!_is_dex_merging || _min_sdk_version >= default_min_sdk_version)
+
     # For D8's backported method desugaring to work properly, the dex merge step
     # must not be set to a higher minSdkVersion than it was for the libraries.
     if (_enable_desugar && _is_dex_merging) {
@@ -1413,13 +1416,14 @@ if (enable_java_templates) {
         }
       }
     } else {  # !_proguard_enabled
+      _is_library = defined(invoker.is_library) && invoker.is_library
       _input_class_jars = []
       if (defined(invoker.input_class_jars)) {
         _input_class_jars = invoker.input_class_jars
       }
       _deps = invoker.deps
 
-      if (_is_dex_merging && enable_bazel_desugar) {
+      if (!_is_library && enable_bazel_desugar) {
         # It would be more efficient to use the pre-dex'ed copy of the runtime,
         # but it's easier to add it in this way.
         _deps += [ "//third_party/bazel/desugar:desugar_runtime_java" ]
@@ -1537,11 +1541,10 @@ if (enable_java_templates) {
             deps += [ ":${_main_dex_list_target_name}" ]
             inputs += [ _main_dex_list_path ]
           }
-        } else if (defined(invoker.enable_library_multidex) &&
-                   invoker.enable_library_multidex) {
-          args += [ "--multi-dex" ]
         }
-
+        if (_is_library) {
+          args += [ "--library" ]
+        }
         if (defined(invoker.input_dex_filearg)) {
           inputs += [ invoker.build_config ]
           args += [ "--dex-inputs-filearg=${invoker.input_dex_filearg}" ]
@@ -1579,7 +1582,7 @@ if (enable_java_templates) {
         # 1) not require recompiles when toggling is_java_debug,
         # 2) allow incremental_install=1 to still have local variable
         #    information even when is_java_debug=false.
-        if (!is_java_debug && _is_dex_merging) {
+        if (!is_java_debug && !_is_library) {
           args += [ "--release" ]
         }
 
@@ -3252,8 +3255,6 @@ if (enable_java_templates) {
   #    from the final .jar file.
   #  jar_included_patterns: Optional list of .class file patterns to include
   #    in the final .jar file. jar_excluded_patterns take precedence over this.
-  #  min_sdk_version: Optional. The minimum Android SDK version this target
-  #    supports.
   #
   # For 'android_apk' and 'android_app_bundle_module' targets only:
   #
@@ -3789,10 +3790,8 @@ if (enable_java_templates) {
               deps += _classpath_deps + [ ":$_header_target_name" ]
             }
 
-            # 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
+            is_library = true
           }
           _public_deps += [ ":${target_name}__dex" ]
         }

build/config/android/rules.gni

@@ -2430,9 +2430,7 @@ if (enable_java_templates) {
 
     _final_deps = []
 
-    _enable_main_dex_list =
-        _enable_multidex &&
-        (!defined(invoker.min_sdk_version) || invoker.min_sdk_version < 21)
+    _enable_main_dex_list = _enable_multidex && _min_sdk_version < 21
     if (_enable_main_dex_list) {
       _generated_proguard_main_dex_config =
           "$_base_path.resources.main-dex-proguard.txt"
@@ -2927,12 +2925,16 @@ if (enable_java_templates) {
           deps += _deps + [ ":$_compile_resources_target" ]
           proguard_mapping_path = _proguard_mapping_path
           proguard_sourcefile_suffix = "$android_channel-$_version_code"
-        } else {
+        } else if (_min_sdk_version >= default_min_sdk_version) {
+          # Enable dex merging only when min_sdk_version is >= what the library
+          # .dex files were created with.
           input_dex_filearg =
               "@FileArg(${_rebased_build_config}:final_dex:all_dex_files)"
           if (_enable_main_dex_list) {
             main_dex_list_input_classes_filearg = "@FileArg(${_rebased_build_config}:deps_info:java_runtime_classpath)"
           }
+        } else {
+          input_classes_filearg = "@FileArg($_rebased_build_config:deps_info:java_runtime_classpath)"
         }
 
         if (_is_static_library_provider) {

chrome/test/android/browsertests_apk/AndroidManifest.xml.jinja2

@@ -10,7 +10,6 @@
     xmlns:tools="http://schemas.android.com/tools"
     package="org.chromium.android_browsertests_apk">
 
-    <uses-sdk android:minSdkVersion="19" android:targetSdkVersion="23" />
     <uses-feature android:glEsVersion="0x00020000" />
 
     <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>

components/cronet/android/BUILD.gn

@@ -1110,6 +1110,7 @@ if (!is_component_build) {
       "cronet_smoketests_missing_native_library_instrumentation_apk") {
     apk_name = "MissingNativeLibrarySmokeTestInstrumentation"
     android_manifest = "test/javatests/AndroidManifest.xml"
+    min_sdk_version = _cronet_min_sdk_version
 
     sources = cronet_smoketests_native_common_srcs + [ "test/smoketests/src/org/chromium/net/smoke/MissingNativeLibraryTest.java" ]
     deps = [
@@ -1179,6 +1180,7 @@ if (!is_component_build) {
   }
 
   test("cronet_unittests_android") {
+    min_sdk_version = _cronet_min_sdk_version
     deps = [
       ":cronet_impl_native_base_java",
       ":cronet_static",
@@ -1204,6 +1206,7 @@ if (!is_component_build) {
   }
 
   test("cronet_tests_android") {
+    min_sdk_version = _cronet_min_sdk_version
     deps = [
       ":cronet_impl_native_base_java",
       ":cronet_static",