Reland "Add synthetic field trial for isolated splits"

This is a reland of 86c3def7

Changed this to use a field on BuildConfig.java so it wouldn't change
the native lib.

Original change's description:
> Add synthetic field trial for isolated splits
>
> This should make analysis easier for a binary experiment, since the
> Finch dashboard can be used.
>
> Bug: 1150162
> Change-Id: Id90204398234938c441982d5c2bc5c6f7c63d575
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2545874
> Commit-Queue: Clark DuVall <cduvall@chromium.org>
> Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#829494}

Bug: 1150162
Change-Id: I9447c7f5e1303f036545287738028443c67551d4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2554032Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
Reviewed-by: Peter Wen <wnwen@chromium.org>
Commit-Queue: Clark DuVall <cduvall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#830242}

base/android/bundle_utils.cc

@@ -66,8 +66,12 @@ std::string BundleUtils::ResolveLibraryPath(const std::string& library_name,
 
 // static
 bool BundleUtils::IsBundle() {
-  return Java_BundleUtils_isBundleForNative(
-      base::android::AttachCurrentThread());
+  return Java_BundleUtils_isBundleForNative(AttachCurrentThread());
+}
+
+// static
+bool BundleUtils::IsolatedSplitsEnabled() {
+  return Java_BundleUtils_isolatedSplitsEnabled(AttachCurrentThread());
 }
 
 // static

base/android/bundle_utils.h

@@ -18,6 +18,9 @@ class BASE_EXPORT BundleUtils {
   // Returns true if the current build is a bundle.
   static bool IsBundle();
 
+  // Returns true if isolated splits are enabled.
+  static bool IsolatedSplitsEnabled();
+
   // Helper function asking Java to resolve a library path. This is required for
   // resolving a module library made available via SplitCompat, rather than in
   // its eventual fully-installed state.

base/android/java/src/org/chromium/base/BundleUtils.java

@@ -65,6 +65,11 @@ public final class BundleUtils {
         sIsBundle = isBundle;
     }
 
+    @CalledByNative
+    public static boolean isolatedSplitsEnabled() {
+        return BuildConfig.ISOLATED_SPLITS_ENABLED;
+    }
+
     /**
      * Returns whether splitName is installed. Note, this will return false on Android versions
      * below O, where isolated splits are not supported.

base/android/java/templates/BuildConfig.template

@@ -86,4 +86,10 @@ public class BuildConfig {
 #else
     public static MAYBE_FINAL boolean IS_CHROMECAST_BRANDING_INTERNAL MAYBE_FALSE;
 #endif
+
+#if defined(_ISOLATED_SPLITS_ENABLED)
+    public static MAYBE_FINAL boolean ISOLATED_SPLITS_ENABLED = true;
+#else
+    public static MAYBE_FINAL boolean ISOLATED_SPLITS_ENABLED MAYBE_FALSE;
+#endif
 }

build/config/android/rules.gni

@@ -1935,6 +1935,7 @@ if (enable_java_templates) {
   #   bundles_supported: Whether or not this target can be treated as a bundle.
   #   resources_version_variable:
   #   is_incremental_install:
+  #   isolated_splits_enabled: Value for ISOLATED_SPLITS_ENABLED.
   template("generate_build_config_srcjar") {
     java_cpp_template(target_name) {
       sources = [ "//base/android/java/templates/BuildConfig.template" ]
@@ -1961,6 +1962,11 @@ if (enable_java_templates) {
         defines += [ "_BUNDLES_SUPPORTED" ]
       }
 
+      if (defined(invoker.isolated_splits_enabled) &&
+          invoker.isolated_splits_enabled) {
+        defines += [ "_ISOLATED_SPLITS_ENABLED" ]
+      }
+
       if (defined(invoker.is_incremental_install) &&
           invoker.is_incremental_install) {
         defines += [ "_IS_INCREMENTAL_INSTALL" ]
@@ -2702,7 +2708,11 @@ if (enable_java_templates) {
 
     if (_generate_buildconfig_java) {
       generate_build_config_srcjar("${_template_name}__build_config_srcjar") {
-        forward_variables_from(invoker, [ "min_sdk_version" ])
+        forward_variables_from(invoker,
+                               [
+                                 "min_sdk_version",
+                                 "isolated_splits_enabled",
+                               ])
         _bundles_supported = _is_bundle_module || _is_static_library_provider
         if (defined(invoker.bundles_supported)) {
           _bundles_supported = invoker.bundles_supported
@@ -3628,6 +3638,7 @@ if (enable_java_templates) {
                                "generate_buildconfig_java",
                                "generate_final_jni",
                                "input_jars_paths",
+                               "isolated_splits_enabled",
                                "is_base_module",
                                "jacoco_never_instrument",
                                "jar_excluded_patterns",

chrome/android/chrome_public_apk_tmpl.gni

@@ -528,6 +528,9 @@ template("monochrome_public_common_apk_or_module_tmpl") {
 
       # Add all loadable modules and shared libraries from DFMs.
       if (_enable_chrome_module) {
+        # Sets ISOLATED_SPLITS_ENABLED in BuildConfig.java.
+        isolated_splits_enabled = true
+
         # The arcore manifest needs to be merged into the base module because the Play
         # Store verifies the com.google.ar.core.min_apk_version meta-data tag is in
         # the base manifest.
@@ -790,6 +793,7 @@ template("monochrome_public_common_apk_or_module_tmpl") {
       "deps",
       "is_monochrome",
       "is_trichrome",
+      "isolated_splits_enabled",
       "loadable_modules",
       "native_lib_placeholders",
       "negative_main_dex_globs",

chrome/browser/chrome_browser_field_trials.cc

@@ -26,6 +26,8 @@
 #include "components/version_info/version_info.h"
 
 #if defined(OS_ANDROID)
+#include "base/android/build_info.h"
+#include "base/android/bundle_utils.h"
 #include "chrome/browser/chrome_browser_field_trials_mobile.h"
 #include "chrome/browser/flags/android/cached_feature_flags.h"
 #include "chrome/common/chrome_features.h"
@@ -133,6 +135,18 @@ void ChromeBrowserFieldTrials::RegisterSyntheticTrials() {
   static constexpr char kEarlyLibraryLoadTrial[] = "EarlyLibraryLoadSynthetic";
   ChromeMetricsServiceAccessor::RegisterSyntheticFieldTrial(
       kEarlyLibraryLoadTrial, group_name);
+
+  // If isolated splits are enabled at build time, Monochrome and Trichrome will
+  // have a different bundle layout, so measure N+ even though isolated splits
+  // are only supported by Android in O+.
+  if (base::android::BuildInfo::GetInstance()->sdk_int() >=
+      base::android::SDK_VERSION_NOUGAT) {
+    static constexpr char kIsolatedSplitsTrial[] = "IsolatedSplitsSynthetic";
+    ChromeMetricsServiceAccessor::RegisterSyntheticFieldTrial(
+        kIsolatedSplitsTrial,
+        base::android::BundleUtils::IsolatedSplitsEnabled() ? "Enabled"
+                                                            : "Disabled");
+  }
 #endif  // defined(OS_ANDROID)
 }