Allow extractCommonProperties to return an error

Refactoring in preparation for follow up changes.

Also:
* Adds a new AssertErrorMessageEquals() helper method.
* Improved error reporting in the accessor and added name to
  extractorProperty to ensure meaningful errors are reported.
* Added String() string method to propertiesContainer.
* Reports errors using the field name as the errors are not really
  fixable by developers and it is more meaningful to the build team.

Bug: 155628860
Test: m nothing
Change-Id: I5c5b8436bcbc39e4e7cd35df2577b2dac53e702a

sdk/sdk_test.go

@@ -231,6 +231,7 @@ type EmbeddedPropertiesStruct struct {
 }
 
 type testPropertiesStruct struct {
+	name        string
 	private     string
 	Public_Kept string `sdk:"keep"`
 	S_Common    string
@@ -246,10 +247,17 @@ func (p *testPropertiesStruct) optimizableProperties() interface{} {
 	return p
 }
 
+func (p *testPropertiesStruct) String() string {
+	return p.name
+}
+
+var _ propertiesContainer = (*testPropertiesStruct)(nil)
+
 func TestCommonValueOptimization(t *testing.T) {
-	common := &testPropertiesStruct{}
+	common := &testPropertiesStruct{name: "common"}
 	structs := []propertiesContainer{
 		&testPropertiesStruct{
+			name:        "struct-0",
 			private:     "common",
 			Public_Kept: "common",
 			S_Common:    "common",
@@ -264,6 +272,7 @@ func TestCommonValueOptimization(t *testing.T) {
 			},
 		},
 		&testPropertiesStruct{
+			name:        "struct-1",
 			private:     "common",
 			Public_Kept: "common",
 			S_Common:    "common",
@@ -285,6 +294,7 @@ func TestCommonValueOptimization(t *testing.T) {
 	h := TestHelper{t}
 	h.AssertDeepEquals("common properties not correct",
 		&testPropertiesStruct{
+			name:        "common",
 			private:     "",
 			Public_Kept: "",
 			S_Common:    "common",
@@ -302,6 +312,7 @@ func TestCommonValueOptimization(t *testing.T) {
 
 	h.AssertDeepEquals("updated properties[0] not correct",
 		&testPropertiesStruct{
+			name:        "struct-0",
 			private:     "common",
 			Public_Kept: "common",
 			S_Common:    "",
@@ -319,6 +330,7 @@ func TestCommonValueOptimization(t *testing.T) {
 
 	h.AssertDeepEquals("updated properties[1] not correct",
 		&testPropertiesStruct{
+			name:        "struct-1",
 			private:     "common",
 			Public_Kept: "common",
 			S_Common:    "",