Implement Composition interface for IME API

LayoutTests/fast/ime/inputmethodcontext-composition-expected.txt

Index: LayoutTests/fast/ime/inputmethodcontext-composition-expected.txt
diff --git a/LayoutTests/fast/ime/inputmethodcontext-composition-expected.txt b/LayoutTests/fast/ime/inputmethodcontext-composition-expected.txt
new file mode 100644
index 0000000000000000000000000000000000000000..19d32947d46f573525ad4bb89384f94c22458897
--- /dev/null
+++ b/LayoutTests/fast/ime/inputmethodcontext-composition-expected.txt
@@ -0,0 +1,40 @@
+This tests composition attribute of InputMethodContext.
+
+On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
+
+
+PASS composition.text is ""
+PASS composition2.text is ""
+Testing IME on an input element.
+PASS composition.text is "abcde"
+PASS composition2.text is ""
+PASS composition.selectionStart is 1
+PASS composition.selectionEnd is 4
+PASS composition.getSegments().length is 3
+PASS composition.getSegments().length is 2
+PASS composition.getSegments().length is 2
+PASS composition.text is ""
+PASS composition.getSegments().length is 0
+PASS input.value is "abcde"
+PASS input2.value is ""
+Testing IME on another input element.
+PASS input.value is "abcde"
+PASS input2.value is ""
+PASS composition.getSegments().length is 0
+PASS composition2.getSegments().length is 1
+PASS input.value is "abcde"
+PASS input2.value is "fghij"
+PASS composition.text is ""
+PASS composition2.text is "fghij"
+PASS composition2.text is ""
+PASS input.value is "abcde"
+PASS input2.value is "fghij"
+Testing when context is obtained after some IME input.
+PASS input3.value is ""
+PASS input3.value is "klmno"
+PASS composition3.text is "klmno"
+PASS composition3.text is ""
+PASS successfullyParsed is true
+
+TEST COMPLETE
+