java_sdk_library: Allow creation of impl shared library to be disabled

Most modules will be providing their implementations via APEX and so do
not need to create an implementation shared library as part of this.

Adds an api_only property which will:
* Prevent the creation of the implementation library.
* Prevent the creation of the .xml file needed at runtime to make
  the shared library available.
* Prevent the library being added to the list of java sdk libraries
  used by make to handle installation.

Bug: 145998881
Test: m checkbuild
Change-Id: Ida5e46a81aa5b0a041882d90d5f362ec79fdddb2
diff --git a/java/sdk_library.go b/java/sdk_library.go
index c68a3d1..057586f 100644
--- a/java/sdk_library.go
+++ b/java/sdk_library.go
@@ -110,6 +110,9 @@
 	// Defaults to "api".
 	Api_dir *string
 
+	// If set to true there is no runtime library.
+	Api_only *bool
+
 	// local files that are used within user customized droiddoc options.
 	Droiddoc_option_files []string
 
@@ -183,7 +186,10 @@
 }
 
 func (module *SdkLibrary) GenerateAndroidBuildActions(ctx android.ModuleContext) {
-	module.Library.GenerateAndroidBuildActions(ctx)
+	// Don't build an implementation library if this is api only.
+	if !proptools.Bool(module.sdkLibraryProperties.Api_only) {
+		module.Library.GenerateAndroidBuildActions(ctx)
+	}
 
 	module.buildPermissionsFile(ctx)
 
@@ -247,6 +253,9 @@
 }
 
 func (module *SdkLibrary) AndroidMkEntries() []android.AndroidMkEntries {
+	if proptools.Bool(module.sdkLibraryProperties.Api_only) {
+		return nil
+	}
 	entriesList := module.Library.AndroidMkEntries()
 	entries := &entriesList[0]
 	entries.Required = append(entries.Required, module.xmlFileName())
@@ -773,16 +782,18 @@
 		// for test API stubs
 		module.createStubsLibrary(mctx, apiScopeTest)
 		module.createStubsSources(mctx, apiScopeTest)
-
-		// for runtime
-		module.createXmlFile(mctx)
 	}
 
-	// record java_sdk_library modules so that they are exported to make
-	javaSdkLibraries := javaSdkLibraries(mctx.Config())
-	javaSdkLibrariesLock.Lock()
-	defer javaSdkLibrariesLock.Unlock()
-	*javaSdkLibraries = append(*javaSdkLibraries, module.BaseModuleName())
+	if !proptools.Bool(module.sdkLibraryProperties.Api_only) {
+		// for runtime
+		module.createXmlFile(mctx)
+
+		// record java_sdk_library modules so that they are exported to make
+		javaSdkLibraries := javaSdkLibraries(mctx.Config())
+		javaSdkLibrariesLock.Lock()
+		defer javaSdkLibrariesLock.Unlock()
+		*javaSdkLibraries = append(*javaSdkLibraries, module.BaseModuleName())
+	}
 }
 
 func (module *SdkLibrary) InitSdkLibraryProperties() {