Fix spacing on welcome screen for small screen (iPhone 4)

Shift the welcome screen contents up to allow for correct spacing when
the full screen size is too small to align the contents in the center
and the bottom button with the button on the next screen.

BUG=721916

Review-Url: https://codereview.chromium.org/2914013002
Cr-Commit-Position: refs/heads/master@{#476326}

ios/chrome/browser/ui/first_run/welcome_to_chrome_view.mm

@@ -45,7 +45,7 @@ const CGFloat kContainerViewCompactWidthPercentage = 0.8;
 // Layout constants.
 const CGFloat kImageTopPadding[SIZE_CLASS_COUNT] = {32.0, 50.0};
 const CGFloat kTOSLabelTopPadding[SIZE_CLASS_COUNT] = {34.0, 40.0};
-const CGFloat kOptInLabelTopPadding[SIZE_CLASS_COUNT] = {10.0, 14.0};
+const CGFloat kOptInLabelPadding[SIZE_CLASS_COUNT] = {10.0, 14.0};
 const CGFloat kCheckBoxPadding[SIZE_CLASS_COUNT] = {10.0, 16.0};
 const CGFloat kOKButtonBottomPadding[SIZE_CLASS_COUNT] = {32.0, 32.0};
 const CGFloat kOKButtonHeight[SIZE_CLASS_COUNT] = {36.0, 54.0};
@@ -326,8 +326,10 @@ NSString* const kCheckBoxCheckedImageName = @"checkbox_checked";
   [self layoutTOSLabel];
   [self layoutOptInLabel];
   [self layoutCheckBoxButton];
-  [self layoutContainerView];
+  // The OK Button must be laid out before the container view so that the
+  // container view can take its position into account.
   [self layoutOKButton];
+  [self layoutContainerView];
 }
 
 - (void)layoutTitleLabel {
@@ -398,7 +400,7 @@ NSString* const kCheckBoxCheckedImageName = @"checkbox_checked";
 
 - (void)layoutOptInLabel {
   // The opt in label is laid out to the right (or left in RTL) of the check box
-  // button and below |TOSLabel| as specified by kOptInLabelTopPadding.
+  // button and below |TOSLabel| as specified by kOptInLabelPadding.
   CGSize checkBoxSize =
       [self.checkBoxButton imageForState:self.checkBoxButton.state].size;
   CGFloat checkBoxPadding = kCheckBoxPadding[self.cr_widthSizeClass];
@@ -407,7 +409,7 @@ NSString* const kCheckBoxCheckedImageName = @"checkbox_checked";
       sizeThatFits:CGSizeMake(CGRectGetWidth(self.containerView.bounds) -
                                   optInLabelSidePadding,
                               CGFLOAT_MAX)];
-  CGFloat optInLabelTopPadding = kOptInLabelTopPadding[self.cr_heightSizeClass];
+  CGFloat optInLabelTopPadding = kOptInLabelPadding[self.cr_heightSizeClass];
   CGFloat optInLabelOriginX =
       base::i18n::IsRTL() ? 0.0f : optInLabelSidePadding;
   self.optInLabel.frame = AlignRectOriginAndSizeToPixels(
@@ -447,12 +449,18 @@ NSString* const kCheckBoxCheckedImageName = @"checkbox_checked";
 - (void)layoutContainerView {
   // The container view is resized according to the final layout of
   // |checkBoxButton|, which is its lowest subview.  The resized view is then
-  // centered horizontally and vertically.
+  // centered horizontally and vertically. If necessary, it is shifted up to
+  // allow |kOptInLabelPadding| between |optInLabel| and |OKButton|.
   CGSize containerViewSize = self.containerView.bounds.size;
   containerViewSize.height = CGRectGetMaxY(self.checkBoxButton.frame);
-  self.containerView.frame = AlignRectOriginAndSizeToPixels(CGRectMake(
-      (CGRectGetWidth(self.bounds) - containerViewSize.width) / 2.0,
+
+  CGFloat padding = kOptInLabelPadding[self.cr_heightSizeClass];
+  CGFloat originY = fmin(
       (CGRectGetHeight(self.bounds) - containerViewSize.height) / 2.0,
+      CGRectGetMinY(self.OKButton.frame) - padding - containerViewSize.height);
+
+  self.containerView.frame = AlignRectOriginAndSizeToPixels(CGRectMake(
+      (CGRectGetWidth(self.bounds) - containerViewSize.width) / 2.0, originY,
       containerViewSize.width, CGRectGetMaxY(self.checkBoxButton.frame)));
 }