Avoid saturation when computing LayoutSize aspect ratio.

8k video could cause LayoutUnit to saturate multiplication when
computing the correct aspect ratio.  This CL does the calculation in
floating point, instead.

Bug: 728303
Test: LayoutSizeTest
Change-Id: I632777e2f140b8203577b3e5e0761f3e7f891aa2
Reviewed-on: https://chromium-review.googlesource.com/773108Reviewed-by: Philip Rogers <pdr@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: Frank Liberato <liberato@chromium.org>
Cr-Commit-Position: refs/heads/master@{#519784}

third_party/WebKit/Source/platform/BUILD.gn

@@ -1802,6 +1802,7 @@ jumbo_source_set("blink_platform_unittests_sources") {
     "geometry/IntRectTest.cpp",
     "geometry/LayoutRectOutsetsTest.cpp",
     "geometry/LayoutRectTest.cpp",
+    "geometry/LayoutSizeTest.cpp",
     "geometry/RegionTest.cpp",
     "graphics/BitmapImageTest.cpp",
     "graphics/CompositorElementIdTest.cpp",

third_party/WebKit/Source/platform/geometry/LayoutSize.h

@@ -133,13 +133,17 @@ class PLATFORM_EXPORT LayoutSize {
 
   LayoutSize FitToAspectRatio(const LayoutSize& aspect_ratio,
                               AspectRatioFit fit) const {
-    float height_scale = Height().ToFloat() / aspect_ratio.Height().ToFloat();
-    float width_scale = Width().ToFloat() / aspect_ratio.Width().ToFloat();
-    if ((width_scale > height_scale) != (fit == kAspectRatioFitGrow))
-      return LayoutSize(Height() * aspect_ratio.Width() / aspect_ratio.Height(),
-                        Height());
-    return LayoutSize(Width(),
-                      Width() * aspect_ratio.Height() / aspect_ratio.Width());
+    const float height_float = Height().ToFloat();
+    const float width_float = Width().ToFloat();
+    float height_scale = height_float / aspect_ratio.Height().ToFloat();
+    float width_scale = width_float / aspect_ratio.Width().ToFloat();
+    if ((width_scale > height_scale) != (fit == kAspectRatioFitGrow)) {
+      return LayoutSize(
+          height_float * aspect_ratio.Width() / aspect_ratio.Height(),
+          Height());
+    }
+    return LayoutSize(
+        Width(), width_float * aspect_ratio.Height() / aspect_ratio.Width());
   }
 
   LayoutSize Fraction() const {

third_party/WebKit/Source/platform/geometry/LayoutSizeTest.cpp

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "platform/geometry/LayoutSize.h"
+
+#include "platform/wtf/text/WTFString.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace blink {
+
+TEST(LayoutSizeTest, FitToAspectRatioDoesntOverflow) {
+  // FitToAspectRatio() shouldn't overflow due to intermediate calculations,
+  // for both the "constrained by width" and "constrained by height" cases.
+  LayoutSize aspect_ratio(50000, 50000);
+  EXPECT_EQ("1000x1000",
+            LayoutSize(2000, 1000)
+                .FitToAspectRatio(aspect_ratio, kAspectRatioFitShrink)
+                .ToString());
+
+  LayoutSize size(1000, 2000);
+  EXPECT_EQ("1000x1000",
+            LayoutSize(1000, 2000)
+                .FitToAspectRatio(aspect_ratio, kAspectRatioFitShrink)
+                .ToString());
+}
+
+}  // namespace blink