Fix integer truncation in Region::Area, and return uint64_t.

Bug: 581518
Change-Id: Icaaf62a88941961421f64454a06e9a53c4c39eee
Reviewed-on: https://chromium-review.googlesource.com/c/1349849Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Commit-Queue: Steve Kobes <skobes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610677}

third_party/blink/renderer/platform/geometry/region.cc

@@ -100,8 +100,8 @@ bool Region::Intersects(const Region& region) const {
                                                                  region.shape_);
 }
 
-double Region::Area() const {
-  double area = 0.0;
+uint64_t Region::Area() const {
+  uint64_t area = 0;
   for (Shape::SpanIterator span = shape_.SpansBegin(), end = shape_.SpansEnd();
        span != end && span + 1 != end; ++span) {
     int height = (span + 1)->y - span->y;
@@ -110,7 +110,7 @@ double Region::Area() const {
                                 end = shape_.SegmentsEnd(span);
          segment != end && segment + 1 != end; segment += 2) {
       int width = *(segment + 1) - *segment;
-      area += height * width;
+      area += (uint64_t)height * (uint64_t)width;
     }
   }
   return area;

third_party/blink/renderer/platform/geometry/region.h

@@ -71,7 +71,7 @@ class PLATFORM_EXPORT Region {
   // Returns true if the query region intersects any part of this region.
   bool Intersects(const Region&) const;
 
-  double Area() const;
+  uint64_t Area() const;
 
 #ifndef NDEBUG
   void Dump() const;

third_party/blink/renderer/platform/geometry/region_test.cc

@@ -383,19 +383,22 @@ TEST(RegionTest, unite) {
 
 TEST(RegionTest, Area) {
   Region r;
-  EXPECT_EQ(0.0, r.Area());
+  EXPECT_EQ(0u, r.Area());
 
   r.Unite(IntRect(10, 20, 30, 10));
-  EXPECT_EQ(300.0, r.Area());
+  EXPECT_EQ(300u, r.Area());
 
   r.Unite(IntRect(20, 10, 10, 30));
-  EXPECT_EQ(500.0, r.Area());
+  EXPECT_EQ(500u, r.Area());
 
   r.Unite(IntRect(10, 10, 30, 30));
-  EXPECT_EQ(900.0, r.Area());
+  EXPECT_EQ(900u, r.Area());
 
   r.Subtract(IntRect(20, 20, 10, 10));
-  EXPECT_EQ(800.0, r.Area());
+  EXPECT_EQ(800u, r.Area());
+
+  r.Unite(IntRect(0, 0, 50000, 50000));
+  EXPECT_EQ(2500000000u, r.Area());
 }
 
 }  // namespace blink