Implement `gn analyze`.

tools/gn/filesystem_utils.h

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef TOOLS_GN_FILESYSTEM_UTILS_H_
 #define TOOLS_GN_FILESYSTEM_UTILS_H_
 
 #include <stddef.h>
 
 #include <string>
@@ skipping 82 matching lines @@
                                const ParseNode* origin,
                                Err* err);
 
 // ----------------------------------------------------------------------------
 
 // Returns true if the input string is absolute. Double-slashes at the
 // beginning are treated as source-relative paths. On Windows, this handles
 // paths of both the native format: "C:/foo" and ours "/C:/foo"
 bool IsPathAbsolute(const base::StringPiece& path);
 
+// Returns true if the input string is source-absolute. Source-absolute
+// paths begin with two forward slashes and resolve as if they are
+// relative to the source root.
+bool IsPathSourceAbsolute(const base::StringPiece& path);
+
 // Given an absolute path, checks to see if is it is inside the source root.
 // If it is, fills a source-absolute path into the given output and returns
 // true. If it isn't, clears the dest and returns false.
 //
 // The source_root should be a base::FilePath converted to UTF-8. On Windows,
 // it should begin with a "C:/" rather than being our SourceFile's style
 // ("/C:/"). The source root can end with a slash or not.
 //
 // Note that this does not attempt to normalize slashes in the output.
 bool MakeAbsolutePathRelativeIfPossible(const base::StringPiece& source_root,
@@ skipping 55 matching lines @@
 bool ContentsEqual(const base::FilePath& file_path, const std::string& data);
 
 // Writes given stream contents to the given file if it differs from existing
 // file contents. Returns true if new contents was successfully written or
 // existing file contents doesn't need updating, false on write error. |err| is
 // set on write error if not nullptr.
 bool WriteFileIfChanged(const base::FilePath& file_path,
                         const std::string& data,
                         Err* err);
 
+// Writes given stream contents to the given file. Returns true if data was
+// successfully written, false otherwise. |err| is set on error if not nullptr.
+bool WriteFile(const base::FilePath& file_path, const std::string& data,
+               Err* err);
+
 // -----------------------------------------------------------------------------
 
 enum class BuildDirType {
   // Returns the root toolchain dir rather than the generated or output
   // subdirectories. This is valid only for the toolchain directory getters.
   // Asking for this for a target or source dir makes no sense.
   TOOLCHAIN_ROOT,
 
   // Generated file directory.
   GEN,
@@ skipping 64 matching lines @@
 OutputFile GetBuildDirForTargetAsOutputFile(const Target* target,
                                             BuildDirType type);
 
 // Returns the scope's current directory.
 SourceDir GetScopeCurrentBuildDirAsSourceDir(const Scope* scope,
                                              BuildDirType type);
 // Lack of OutputDir version is due only to it not currently being needed,
 // please add one if you need it.
 
 #endif  // TOOLS_GN_FILESYSTEM_UTILS_H_