Add tests for PeepholeCollectPropertyAssignments covering object an…

…d array spread.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=236004637

test/com/google/javascript/jscomp/PeepholeCollectPropertyAssignmentsTest.java

@@ -59,6 +59,13 @@ public void testArrayOptimization1() {
          "var a = [1, 2, 3];");
   }
 
+  @Test
+  public void testArray_nonConsecutiveAssignments() {
+    test(
+        "var a = []; a[2] = 1; a[0] = 2; a[1] = 3;", //
+        "var a = [2, 3, 1];");
+  }
+
   @Test
   public void testArrayOptimization2() {
     test("var a; a = []; a[0] = 1; a[1] = 2; a[2] = 3;",
@@ -220,6 +227,22 @@ public void testForwardReference2() {
          "var a; a = [1]; a[1] = a;");
   }
 
+  @Test
+  public void testArray_usingSpread_diablesOptimization_leadingSpread() {
+    // TODO(nickreid): A future improvement could generate `var a = [3, ...b, 2];`
+    testSame("var a = [1, ...b, 2]; a[0] = 3;");
+  }
+
+  @Test
+  public void testArray_usingSpread_diablesOptimization_withinSpread() {
+    testSame("var a = [1, ...b, 2]; a[1] = 3;");
+  }
+
+  @Test
+  public void testArray_usingSpread_diablesOptimization_followingSpread() {
+    testSame("var a = [1, ...b, 2]; a[2] = 3;");
+  }
+
   @Test
   public void testObjectOptimization1() {
     test("var o = {}; o.x = 0; o['y'] = 1; o[2] = 2;",
@@ -325,6 +348,23 @@ public void testObjectPropertyReassigned4() {
         "a.b = x+10;");
   }
 
+  @Test
+  public void testObject_usingSpread_diablesOptimization_leadingSpread() {
+    test(
+        "var a = {a: 1, ...b, c: 2}; a.a = 3;", //
+        "var a = {...b, c: 2, a: 3};");
+  }
+
+  @Test
+  public void testObject_usingSpread_diablesOptimization_withinSpread() {
+    testSame("var a = {a: 1, ...b, c: 2, b: 3};");
+  }
+
+  @Test
+  public void testObject_usingSpread_diablesOptimization_followingSpread() {
+    testSame("var a = {a: 1, ...b, c: 3};");
+  }
+
   @Test
   public void testObjectComputedProp1() {
     testSame(