android: Fix rank comparator overflow

Native can pass up std::numeric_limits<unsigned int>::max() as the frame
depth. We store this in a long in java which does not overflow. However
comparator currently does substracts two frame depths and casts it down
to int to get the sign. This can cause int overflow and change the
result. Use Long.signum instead.

Change-Id: Id0591250d4ae588bd3f54964fd53e3211402133a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1610083Reviewed-by: ssid <ssid@chromium.org>
Commit-Queue: Bo <boliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#659779}

content/public/android/java/src/org/chromium/content/browser/ChildProcessRanking.java

@@ -66,7 +66,7 @@ public class ChildProcessRanking implements Iterable<ChildProcessConnection> {
                 return 1;
             }
 
-            return (int) (o1.frameDepth - o2.frameDepth);
+            return Long.signum(o1.frameDepth - o2.frameDepth);
         }
 
         @Override

content/public/android/junit/src/org/chromium/content/browser/ChildProcessRankingTest.java

@@ -229,6 +229,25 @@ public class ChildProcessRankingTest {
         assertInGroupOrderedByImportance(new ChildProcessConnection[] {c1});
     }
 
+    @Test
+    public void testFrameDepthIntOverflow() {
+        ChildProcessConnection c1 = createConnection();
+        ChildProcessConnection c2 = createConnection();
+        ChildProcessConnection c3 = createConnection();
+        ChildProcessRanking ranking = new ChildProcessRanking();
+
+        // Native can pass up the maximum value of unsigned int.
+        long intOverflow = ((long) Integer.MAX_VALUE) * 2;
+        ranking.addConnection(c3, true /* foreground */, intOverflow - 1 /* frameDepth */,
+                true /* intersectsViewport */, ChildProcessImportance.NORMAL);
+        ranking.addConnection(c2, true /* foreground */, 10 /* frameDepth */,
+                true /* intersectsViewport */, ChildProcessImportance.NORMAL);
+        ranking.addConnection(c1, true /* foreground */, intOverflow /* frameDepth */,
+                true /* intersectsViewport */, ChildProcessImportance.NORMAL);
+
+        assertRankingAndRemoveAll(ranking, new ChildProcessConnection[] {c2, c3, c1});
+    }
+
     @Test
     public void testThrowExceptionWhenGoingOverLimit() {
         ChildProcessRanking ranking = new ChildProcessRanking(2);