Update Dart based on dartanalyzer.

Author: NeilFraser

dart/DMPClass.dart

@@ -1401,7 +1401,7 @@ class DiffMatchPatch {
           param = param.replaceAll('+', '%2B');
           try {
             param = Uri.decodeFull(param);
-          } on ArgumentError catch (e) {
+          } on ArgumentError {
             // Malformed URI sequence.
             throw new ArgumentError('Illegal escape in diff_fromDelta: $param');
           }
@@ -1413,7 +1413,7 @@ class DiffMatchPatch {
           int n;
           try {
             n = int.parse(param);
-          } on FormatException catch (e) {
+          } on FormatException {
             throw new ArgumentError('Invalid number in diff_fromDelta: $param');
           }
           if (n < 0) {
@@ -1423,7 +1423,7 @@ class DiffMatchPatch {
           String text;
           try {
             text = text1.substring(pointer, pointer += n);
-          } on RangeError catch (e) {
+          } on RangeError {
             throw new ArgumentError('Delta length ($pointer)'
                 ' larger than source text length (${text1.length}).');
           }
@@ -2163,7 +2163,7 @@ class DiffMatchPatch {
           String line;
           try {
             line = Uri.decodeFull(text[textPointer].substring(1));
-          } on ArgumentError catch (e) {
+          } on ArgumentError {
             // Malformed URI sequence.
             throw new ArgumentError('Illegal escape in patch_fromText: $line');
           }

dart/DiffClass.dart

@@ -52,6 +52,19 @@ class Diff {
    * [other] is another Diff to compare against.
    * Returns true or false.
    */
-  bool operator ==(Diff other) =>
-      operation == other.operation && text == other.text;
+  @override
+  bool operator ==(Object other) =>
+  	      identical(this, other) ||
+          other is Diff &&
+              runtimeType == other.runtimeType &&
+              operation == other.operation &&
+              text == other.text;
+
+  /**
+   * Generate a uniquely identifiable hashcode for this Diff.
+   * Returns numeric hashcode.
+   */
+  @override
+  int get hashCode =>
+      operation.hashCode ^ text.hashCode;
 }

dart/tests/DiffMatchPatchTest.dart

@@ -16,10 +16,6 @@
  * limitations under the License.
  */
 
-// Can't import DiffMatchPatch library since the private functions would be
-// unavailable.  Instead, import all the source files.
-import 'dart:collection';
-import 'dart:math';
 import '../DiffMatchPatch.dart';
 
 // Expect class disappeared from Dart unexpectedly.  Here's a minimal shim.
@@ -43,7 +39,7 @@ class Expect {
   static void throws(void f(), String msg) {
     try {
       f();
-    } catch (e, s) {
+    } catch (e) {
       return;
     }
     throw new Exception('Expect.throws($msg) fails');