Move files in wtf/ to platform/wtf/ (Part 12).

third_party/WebKit/Source/wtf/ScopedLogger.md

-# Debugging with ScopedLogger
-
-## Overview
-
-ScopedLogger is a logger that shows nested calls by indenting.
-
-For example, if you were debugging a layout issue you could add a ScopedLogger
-to the top of the `LayoutBlock::layout` function:
-
-```c++
-void LayoutBlock::layout()
-{
-    WTF_CREATE_SCOPED_LOGGER(logger, "layout %s", debugName().utf8().data());
-    ...
-```
-
-The arguments of the `WTF_CREATE_SCOPED_LOGGER` macro are the name of the
-object, followed by the first log message, followed by printf-style varargs.
-In the above example, the log message includes the debug name of the block that
-is currently being laid out.
-
-ScopedLogger wraps log messages in parentheses, with indentation proportional to
-the number of instances.  This makes it easy to see the flow of control in the
-output, particularly when instrumenting recursive functions.  Here is some of
-the output of the above example when laying out www.google.com:
-
-```
-( layout LayoutView #document
-  ( layout LayoutBlockFlow HTML
-    ( layout LayoutBlockFlow BODY id='gsr' class='hp vasq'
-      ( layout LayoutBlockFlow (relative positioned) DIV id='viewport' class='ctr-p'
-        ( layout LayoutBlockFlow DIV id='doc-info' )
-        ( layout LayoutBlockFlow DIV id='cst' )
-        ( layout LayoutBlockFlow (positioned) A )
-        ( layout LayoutBlockFlow (positioned) DIV id='searchform' class='jhp' )
-      )
-    )
-  )
-)
-```
-
-## Appending to a ScopedLogger
-
-Every ScopedLogger has an initial log message, which is often sufficient.  But
-you can also write additional messages to an existing ScopedLogger with
-`WTF_APPEND_SCOPED_LOGGER`.  For example:
-
-```c++
-    // further down in LayoutBlock::layout...
-
-    if (needsScrollAnchoring) {
-        WTF_APPEND_SCOPED_LOGGER(logger, "restoring scroll anchor");
-        getScrollableArea()->scrollAnchor().restore();
-    }
-```
-
-## Conditional ScopedLoggers
-
-It's often useful to create a ScopedLogger only if some condition is met.
-Unfortunately, the following doesn't work correctly:
-
-```c++
-void foo() {
-    if (condition) {
-        WTF_CREATE_SCOPED_LOGGER(logger, "foo, with condition");
-        // Oops: logger exits scope prematurely!
-    }
-    bar();  // any ScopedLogger in bar won't nest
-}
-```
-
-To guard a ScopedLogger construction with a condition without restricting its
-scope, use `WTF_CREATE_SCOPED_LOGGER_IF`:
-
-```c++
-void foo() {
-    WTF_CREATE_SCOPED_LOGGER_IF(logger, condition, "message");
-    bar();
-}
-```
-
-## Requirements
-
-The ScopedLogger class and associated macros are defined in
-[Assertions.h](Assertions.h), which most Blink source files already include
-indirectly.  ScopedLogger can't be used outside of Blink code yet.
-
-The ScopedLogger macros work in debug builds by default.  They are compiled out
-of release builds, unless your `GYP_DEFINES` or GN args file includes one of the
-following:
-
-* `dcheck_always_on`: enables assertions and ScopedLogger
-* `blink_logging_always_on`: enables ScopedLogger, but not assertions
-
-The macro names are cumbersome to type, but most editors can be configured to
-make this easier.  For example, you can add the following to a Sublime Text key
-binding file to make Ctrl+Alt+L insert a ScopedLogger:
-
-```
-  { "keys": ["ctrl+alt+l"], "command": "insert",
-    "args": {"characters": "WTF_CREATE_SCOPED_LOGGER(logger, \"msg\");"}
-  }
-```