Take empty arrays into account to break down chunks

Previous implementation assumed 'a' and 'b' to be
undefined, but not empty array.

Change-Id: I7a339d839b0645612f666de973f5563f0c0d6af0

polygerrit-ui/app/elements/diff/gr-diff-processor/gr-diff-processor.ts

diff --git a/polygerrit-ui/app/elements/diff/gr-diff-processor/gr-diff-processor.ts b/polygerrit-ui/app/elements/diff/gr-diff-processor/gr-diff-processor.ts
index c3d758c..5a432dd 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-processor/gr-diff-processor.ts
+++ b/polygerrit-ui/app/elements/diff/gr-diff-processor/gr-diff-processor.ts
@@ -679,15 +679,18 @@
    */
   _breakdownChunk(chunk: DiffContent): DiffContent[] {
     let key: 'a' | 'b' | 'ab' | null = null;
-    if (chunk.a && !chunk.b) {
+    const {a, b, ab, move_details} = chunk;
+    if (a?.length && !b?.length) {
       key = 'a';
-    } else if (chunk.b && !chunk.a) {
+    } else if (b?.length && !a?.length) {
       key = 'b';
-    } else if (chunk.ab) {
+    } else if (ab?.length) {
       key = 'ab';
     }
 
-    if (!key) {
+    // Move chunks should not be divided because of move label
+    // positioned in the top of the chunk
+    if (!key || move_details) {
       return [chunk];
     }
 

polygerrit-ui/app/elements/diff/gr-diff-processor/gr-diff-processor_test.js

diff --git a/polygerrit-ui/app/elements/diff/gr-diff-processor/gr-diff-processor_test.js b/polygerrit-ui/app/elements/diff/gr-diff-processor/gr-diff-processor_test.js
index 5496b62..0c3c9bf 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-processor/gr-diff-processor_test.js
+++ b/polygerrit-ui/app/elements/diff/gr-diff-processor/gr-diff-processor_test.js
@@ -590,6 +590,43 @@
       assert.deepEqual(result[1].ab, content[0].ab.slice(120));
     });
 
+    test('breaks down added chunks', () => {
+      const size = 120 * 2 + 5;
+      const content = _.times(size, () => `${Math.random()}`);
+      element.context = 5;
+      const splitContent = element._splitLargeChunks([{a: [], b: content}])
+          .map(r => r.b);
+      assert.equal(splitContent.length, 3);
+      assert.deepEqual(splitContent[0], content.slice(0, 5));
+      assert.deepEqual(splitContent[1], content.slice(5, 125));
+      assert.deepEqual(splitContent[2], content.slice(125));
+    });
+
+    test('breaks down removed chunks', () => {
+      const size = 120 * 2 + 5;
+      const content = _.times(size, () => `${Math.random()}`);
+      element.context = 5;
+      const splitContent = element._splitLargeChunks([{a: content, b: []}])
+          .map(r => r.a);
+      assert.equal(splitContent.length, 3);
+      assert.deepEqual(splitContent[0], content.slice(0, 5));
+      assert.deepEqual(splitContent[1], content.slice(5, 125));
+      assert.deepEqual(splitContent[2], content.slice(125));
+    });
+
+    test('does not break down moved chunks', () => {
+      const size = 120 * 2 + 5;
+      const content = _.times(size, () => `${Math.random()}`);
+      element.context = 5;
+      const splitContent = element._splitLargeChunks([{
+        a: content,
+        b: [],
+        move_details: {changed: false},
+      }]).map(r => r.a);
+      assert.equal(splitContent.length, 1);
+      assert.deepEqual(splitContent[0], content);
+    });
+
     test('does not break-down common chunks w/ context', () => {
       const content = [{
         ab: _.times(75, () => `${Math.random()}`),