Fix a possible crash when displaying a small HarmonyButton.

Bug: 
Change-Id: Ia6e2432f3b735adc080327ee517f6050859ffbfc
Reviewed-on: https://chromium-review.googlesource.com/974084Reviewed-by: Leonard Grey <lgrey@chromium.org>
Commit-Queue: Sidney San Martín <sdy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#545550}

chrome/browser/ui/cocoa/harmony_button.mm

@@ -222,7 +222,9 @@ constexpr NSTimeInterval kTransitionDuration = 0.25;
   CALayer* layer = self.layer;
   layer.shadowPath =
       base::ScopedCFTypeRef<CGPathRef>(CGPathCreateWithRoundedRect(
-          layer.bounds, layer.cornerRadius, layer.cornerRadius, nullptr));
+          layer.bounds,
+          MIN(layer.cornerRadius, CGRectGetWidth(layer.bounds) / 2),
+          MIN(layer.cornerRadius, CGRectGetHeight(layer.bounds) / 2), nullptr));
   [self updateHoverButtonAppearanceAnimated:NO];
   self.title = self.title;  // Match the theme.
   [super layout];

chrome/browser/ui/cocoa/harmony_button_unittest.mm

@@ -24,6 +24,17 @@ class HarmonyButtonTest : public ui::CocoaTest {
 
 TEST_VIEW(HarmonyButtonTest, button_)
 
+// Verify that displaying a button that's smaller than double the corner radius
+// doesn't crash. (CGPathCreateWithRoundedRect throws an exception if you pass
+// it a radius that's too big).
+TEST_F(HarmonyButtonTest, TooSmall) {
+  CGFloat cornerRadius = button_.layer.cornerRadius;
+  EXPECT_LT(0, cornerRadius);
+  [button_ setFrameSize:NSMakeSize(cornerRadius, cornerRadius)];
+  [button_ layoutSubtreeIfNeeded];
+  [button_ displayIfNeeded];
+}
+
 TEST(HarmonyButtonTestMore, NSViewRespondsToClipsToBounds) {
   // HarmonyButton implements an undocumented method to avoid having its shadow
   // clipped, so verify that it hasn't disappeared.