Set lower bound on contents pane size.

We have had several recent problems with the lower bound on browser
width being driven by the toolbar, which can have its minimum size
change as buttons are hidden or shown, or as elements in the omnibox are
hidden or shown or change size.

The change to the new FlexLayout for the toolbar has made the browser
much more responsive to the toolbar's minimum size, and has resulted in
an overall smaller minimum width for the browser window. This has
created additional problems, such as WebUI pages which have important
content or controls cut off due to not having enough room to render.

This patch kills two birds with one stone - it restores the minimum
width required for our WebUI pages, while also making the contents view
the long tent pole for browser minimum width rather than the toolbar,
which should also solve a number of minor regressions caused by the
switch to declarative layout for the toolbar that were the result of
its minimum size being able to change.

For this CL the value of 500 DIPs was chosen. This is not enough to
display chrome://settings without a horizontal scroll bar, but none of
the UI elements are completely hidden either, and it is also enough to
display the content in WebUI dialogs. The choice of 500 (rather than,
say, 550, which would have accommodated the entire width of WebUI) was
to maintain the tradeoff betwqeen usability and privacy; some users
like to browser certain content in a very small window even on large
screens to prevent others from seeing what they are doing.

Bug: 927708, 927846
Change-Id: Ie30e6dd31d26e01900b4f5ee0a1209164e151e59
Commit-Queue: Dana Fried <>
Reviewed-by: Bret Sepulveda <>
Cr-Commit-Position: refs/heads/master@{#629491}
6 files changed