Add/update READMEs for various directories I own.

As requested in https://bit.ly/chromium-readme-tracker .

Bug: none
Change-Id: Ib25c6c9cb7a72ffbbca308b61295aab6018012ac
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2336181
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#795020}

chrome/browser/ui/README.md

@@ -2,10 +2,13 @@ This directory contains the implementation of the Chromium UI. Code in the root
 of this directory is toolkit- and platform-independent. There are subdirectories
 with implementations for specific toolkits and OSes. Code in the root of this
 directory should *not* be aware of platform-specific implementation details or
-reach into the platform implementation subdirectories.
+reach into the platform implementation subdirectories. This directory also
+should not contain browser-process-scoped items that are not UI-specific, such
+as parts of the startup logic; these sorts of things belong elsewhere in
+chrome/browser/.
 
-This directory is often referred to in conversation as "cbui", pronounced "sea
-bee you eye".
+This directory is often referred to in conversation as "cbui" or "c/b/ui",
+pronounced "sea bee you eye".
 
 Important subdirectories:
 * views - the Views implementation of the UI, used on Windows, Mac, Linux, and
@@ -35,3 +38,8 @@ This pattern often looks like this:
 
 //chrome/browser/ui/android/my_dialog_android.cc:  
     void ShowMyDialog(...) { ... }
+
+Because "Chromium UI" is such a large surface area, do not add new files
+directly to this directory; instead, add subdirectories with more specific
+OWNERS and place new features and files in them. Cleanup of existing scattered
+files is also welcome.

components/country_codes/README.md

+The country codes component deals with 2-letter country codes (aka ISO 3166-1).
+Its primary purpose is to interface with platform-specific functionality to
+provide a unified API to find out "what is the system's current country code".

components/google/README.md

+The Google component deals with Google- (and Google-owned-property-)specific
+URLs and utilities.  This includes functions that determine if URLs are various
+types of Google URLs, getters for Google search URLs, and various URL
+manipulation functions.
+
+Since Chrome should serve users of all search engines, URLs, and products well,
+be hesitant before keying behavior to these functions.  Consider whether the
+proposed behavior would appear innocuous and appealing if you worked for a
+direct Google competitor, as well as whether you'd want a standardized mechanism
+for other sites to achieve the same results.

components/infobars/README

-- Infobars is a layered component
-(https://sites.google.com/a/chromium.org/dev/developers/design-documents/layered-components-design)
-to enable it to be shared cleanly on iOS.
-
-Directory structure:
-core/: shared code that does not depend on src/content/
-content/: Driver for the shared code based on the content layer.

components/infobars/README.md

+The infobars component contains the core types for infobars, a UI surface that
+shows informative but generally nonblocking updates to users related to their
+current page content.  This is used on both desktop and mobile, though the
+presentation and available infobars both differ.  On desktop, for example,
+infobars are a thin bar atop the page, while on Android an "infobar" is a
+larger, popup-like surface at screen bottom.
+
+Infobars are a problematic UI design for various reasons (spoofability,
+dynamically modifying content area size, not being visually anchored and scoped
+well), and are occasionally used for purposes outside their original intent
+(e.g. the "default browser" infobar, which does not relate to the page content).
+Be cautious about adding new ones.
+
+Infobars is a layered component
+(https://sites.google.com/a/chromium.org/dev/developers/design-documents/layered-components-design)
+to enable it to be shared cleanly on iOS.
+
+Directory structure:
+android/: Android-specific specializations
+core/: Shared code that does not depend on src/content/
+content/: Driver for the shared code based on the content layer

components/url_formatter/README.md

+The URL Formatter component contains utilities to convert between URLs and
+human-entered/human-readable strings.  Broadly, consuming human-entered URLs
+happens via "fixup", which tries to make "reasonable" adjustments to strings to
+convert them into URLs (e.g. auto-prepending schemes, but also many more, some
+of which may be surprising).  Producing human-readable URLs happens via
+"formatting", which can strip unimportant parts of the URL, unescape/decode
+sections, etc.
+
+These functions are meant to work in conjunction with the stricter, more limited
+capabilities of GURL, and were originally designed for use with the omnibox,
+though they've since been used in other parts of the UI as well.
+
+Because these functions are powerful, it's possible to introduce security risks
+with incautious use.  Be sure you understand what you need and what they're
+doing before using them; don't just copy existing callers.

components/webdata/README

-WebData is not allowed to depend on content/, because it is used by iOS.
-If dependences on content/ need to be added to WebData, it will have to be made
-into a layered component: see
-http://www.chromium.org/developers/design-documents/layered-components-design
-for more information.

components/webdata/README.md

+The webdata component manages the "web database", a SQLite database stored in
+the user's profile containing various webpage-related metadata such as autofill
+and web search engine data.
+
+This component is not allowed to depend on content/, because it is used by iOS.
+If dependencies on content/ need to be added, this component will have to be
+made into a layered component: see
+https://www.chromium.org/developers/design-documents/layered-components-design .

components/webdata_services/README.md

+The webdata services component contains the wrappers used to access the specific
+services built atop the web database (see //components/webdata/).  Because there
+is a single database instance, the various services accessing different tables
+are created and destroyed together, and this component is what does that tying
+together.