Add integration testing infrastructure

Fix mutator registration for tests to allow different tests
in the same package to register different mutators.

Allow tests to track the resulting ModuleBuildParams objects
to use in assertions, and provide helpers for getting them.
For example:
    config := android.TestConfig(buildDir)
    ctx := android.NewTestContext()
    ctx.RegisterModuleType(...)
    ctx.MockFileSystem(...)
    ctx.ParseBlueprintsFile("Android.bp")
    ctx.PrepareBuildActions(config)
    ctx.Register()
    // Get the Inputs value passed to the javac rule for the foo module
    inputs := ctx.ModuleForTests("foo".Rule("javac").Inputs

Test: java_test.go
Change-Id: I10c82967f5f3586d2c176f169906b571ed82fc73

android/module.go

@@ -111,6 +111,8 @@ type Module interface {
 
 	AddProperties(props ...interface{})
 	GetProperties() []interface{}
+
+	BuildParamsForTests() []ModuleBuildParams
 }
 
 type nameProperties struct {
@@ -291,6 +293,9 @@ type ModuleBase struct {
 	hooks hooks
 
 	registerProps []interface{}
+
+	// For tests
+	buildParams []ModuleBuildParams
 }
 
 func (a *ModuleBase) AddProperties(props ...interface{}) {
@@ -301,6 +306,10 @@ func (a *ModuleBase) GetProperties() []interface{} {
 	return a.registerProps
 }
 
+func (a *ModuleBase) BuildParamsForTests() []ModuleBuildParams {
+	return a.buildParams
+}
+
 // Name returns the name of the module.  It may be overridden by individual module types, for
 // example prebuilts will prepend prebuilt_ to the name.
 func (a *ModuleBase) Name() string {
@@ -520,6 +529,8 @@ func (a *ModuleBase) GenerateBuildActions(ctx blueprint.ModuleContext) {
 			return
 		}
 	}
+
+	a.buildParams = androidCtx.buildParams
 }
 
 type androidBaseContextImpl struct {
@@ -538,6 +549,9 @@ type androidModuleContext struct {
 	checkbuildFiles Paths
 	missingDeps     []string
 	module          Module
+
+	// For tests
+	buildParams []ModuleBuildParams
 }
 
 func (a *androidModuleContext) ninjaError(desc string, outputs []string, err error) {
@@ -566,6 +580,10 @@ func (a *androidModuleContext) Build(pctx blueprint.PackageContext, params bluep
 }
 
 func (a *androidModuleContext) ModuleBuild(pctx blueprint.PackageContext, params ModuleBuildParams) {
+	if a.config.captureBuild {
+		a.buildParams = append(a.buildParams, params)
+	}
+
 	bparams := blueprint.BuildParams{
 		Rule:            params.Rule,
 		Deps:            params.Deps,