servo: Merge #7256 - layout: Use the value of the `max-width` property when speculating what the inline sizes of block formatting contexts are likely to be (from pcwalton:block-formatting-contexts-max-width); r=mbrubeck

Usually, Web developers set this property on block formatting contexts
in order to avoid running into floats, and we can use this as a
speculation hint.

Fixes the width of the search box on the Google SERPs.

r? @mbrubeck

Source-Repo: https://github.com/servo/servo
Source-Revision: 19d466b06250f10169e88fc7f0b447c7f2f8209e

servo/components/layout/block.rs

@@ -1639,10 +1639,16 @@ impl Flow for BlockFlow {
                 // We can't actually compute the inline-size of this block now, because floats
                 // might affect it. Speculate that its inline-size is equal to the inline-size
                 // computed above minus the inline-size of the previous left and/or right floats.
-                self.fragment.border_box.size.inline =
-                    self.fragment.border_box.size.inline -
-                    self.inline_size_of_preceding_left_floats -
-                    self.inline_size_of_preceding_right_floats;
+                //
+                // (If `max-width` is set, then don't perform this speculation. We guess that the
+                // page set `max-width` in order to avoid hitting floats. The search box on Google
+                // SERPs falls into this category.)
+                if self.fragment.style.max_inline_size() == LengthOrPercentageOrNone::None {
+                    self.fragment.border_box.size.inline =
+                        self.fragment.border_box.size.inline -
+                        self.inline_size_of_preceding_left_floats -
+                        self.inline_size_of_preceding_right_floats;
+                }
             }
             FormattingContextType::Other => {
                 self.base.flags.remove(IMPACTED_BY_LEFT_FLOATS);