Allow building with isolated splits enabled without chrome module

This will allow testing with only isolated splits enabled, which will be
a useful configuration for perf testing, and a backup plan if the chrome
module ends up needing more work.

Bug: 1151538
Change-Id: I2db5ec610d9f1c21c0b9bca607cf51ad6ad3b85a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2553222Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Clark DuVall <cduvall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#830826}

chrome/android/chrome_public_apk_tmpl.gni

@@ -526,11 +526,13 @@ template("monochrome_public_common_apk_or_module_tmpl") {
         }
       }
 
+      # Sets ISOLATED_SPLITS_ENABLED in BuildConfig.java.
+      if (_is_bundle_module) {
+        isolated_splits_enabled = enable_isolated_splits
+      }
+
       # 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.

chrome/android/java/AndroidManifest.xml

@@ -14,7 +14,8 @@ by a child template that "extends" this file.
     xmlns:tools="http://schemas.android.com/tools"
     package="{{ manifest_package }}"
     {% set definitions_in_split = definitions_in_split|default(0) == 'true' %}
-    {% if definitions_in_split %}
+    {% set enable_isolated_splits = enable_isolated_splits|default(0) == 'true' %}
+    {% if enable_isolated_splits %}
     android:isolatedSplits="true"
     {% endif %}
     tools:ignore="MissingVersion">
@@ -154,7 +155,7 @@ by a child template that "extends" this file.
     <!-- Set android:largeHeap to "true" to allow more than the default
          Java heap limit (32Mb on Nexus S, 48Mb on Xoom). -->
       <application android:name="{% block application_name %}
-          {%- if definitions_in_split -%}
+          {%- if enable_isolated_splits -%}
           org.chromium.chrome.browser.base.SplitChromeApplication
           {%- else -%}
           org.chromium.chrome.browser.ChromeApplication
@@ -177,7 +178,7 @@ by a child template that "extends" this file.
         {% endif %}
         android:networkSecurityConfig="@xml/network_security_config"
         android:allowAudioPlaybackCapture="false"
-        {% if definitions_in_split %}
+        {% if enable_isolated_splits %}
         android:appComponentFactory="org.chromium.chrome.browser.base.SplitCompatAppComponentFactory"
         {% endif %}
         {% block extra_application_attributes %}{% endblock %}>

chrome/android/java/AndroidManifest_monochrome.xml

@@ -9,7 +9,7 @@
 ##
 
 {% block application_name %}
-{%- if definitions_in_split -%}
+{%- if enable_isolated_splits -%}
 org.chromium.chrome.browser.base.SplitMonochromeApplication
 {%- else -%}
 org.chromium.chrome.browser.MonochromeApplication

chrome/android/java/src/org/chromium/chrome/browser/base/SplitCompatUtils.java

@@ -18,6 +18,7 @@ import org.chromium.base.annotations.IdentifierNameString;
 
 /** Utils for compatibility with isolated splits. */
 public class SplitCompatUtils {
+    private static final String CHROME_SPLIT_NAME = "chrome";
     private static final ArraySet<ClassLoader> sInflationClassLoaders = new ArraySet<>();
 
     private SplitCompatUtils() {}
@@ -33,7 +34,10 @@ public class SplitCompatUtils {
 
     /** Creates a context which can be used to load code and resources in the chrome split. */
     public static Context createChromeContext(Context base) {
-        return BundleUtils.createIsolatedSplitContext(base, "chrome");
+        if (!BundleUtils.isIsolatedSplitInstalled(base, CHROME_SPLIT_NAME)) {
+            return base;
+        }
+        return BundleUtils.createIsolatedSplitContext(base, CHROME_SPLIT_NAME);
     }
 
     /**

chrome/android/modules/buildflags.gni

@@ -21,6 +21,12 @@ declare_args() {
   enable_chrome_child_modules = true
 }
 
+declare_args() {
+  # Whether isolated splits are enabled. This can be enabled/disabled separately
+  # from enable_chrome_module to test performance in various configurations.
+  enable_isolated_splits = enable_chrome_module
+}
+
 # If true, lld is used to partition feature code into separate libraries, which
 # in turn are included in Dynamic Feature Modules.
 use_native_partitions = is_android && is_clang && use_lld && !is_component_build

chrome/android/monochrome_android_manifest_jinja_variables.gni

@@ -2,10 +2,13 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//chrome/android/modules/buildflags.gni")
+
 use_32bit_abi_jinja_variable = "use32bitAbi=android:use32bitAbi=\"true\""
 
 monochrome_android_manifest_jinja_variables = [
   "min_sdk_version=24",
   "sandboxed_service_exported=true",
   use_32bit_abi_jinja_variable,
+  "enable_isolated_splits=$enable_isolated_splits",
 ]

chrome/android/trichrome.gni

@@ -6,6 +6,7 @@ import("//build/config/android/config.gni")
 import("//build/config/android/rules.gni")
 import("//build/util/version.gni")
 import("//chrome/android/chrome_public_apk_tmpl.gni")
+import("//chrome/android/modules/buildflags.gni")
 
 if (!defined(default_trichrome_certdigest)) {
   default_trichrome_certdigest =
@@ -32,6 +33,7 @@ trichrome_jinja_variables = [
   "trichrome_library=$trichrome_library_package",
   "trichrome_certdigest=$trichrome_certdigest",
   "use32bitAbi=android:use32bitAbi=\"true\"",
+  "enable_isolated_splits=$enable_isolated_splits",
 ]
 
 trichrome_synchronized_proguard =