Added the preprocess scripts.

eng/common/scripts/Verify-Links.ps1

@@ -30,6 +30,7 @@ function NormalizeUrl([string]$url){
     $url = "file://" + (Resolve-Path $url).ToString();
   }
 
+  Write-Verbose "The url to check against: $url."
   $uri = [System.Uri]$url;
 
   if ($script:baseUrl -eq "") {

eng/common/scripts/get-markdown-files-from-changed-files.ps1

@@ -0,0 +1,49 @@
+param (
+  # The root repo we scaned with.
+  [string[]] $RootRepo = '$PSScriptRoot/../../..',
+  # The target branch to compare with.
+  [string] $targetBranch = "origin/${env:SYSTEM_PULLREQUEST_TARGETBRANCH}"
+)
+$deletedFiles = (git diff $targetBranch HEAD --name-only --diff-filter=D)
+$renamedFiles = (git diff $targetBranch HEAD --diff-filter=R)
+$changedMarkdowns = (git diff $targetBranch HEAD --name-only -- '*.md')
+
+$beforeRenameFiles = @()
+# Retrieve the 'renamed from' files. Git command only returns back the files after rename. 
+# In order to have the files path before rename, it has to do some regex checking. 
+# It is better to be replaced by more reliable commands if any.
+foreach ($file in $renamedFiles) {
+  if ($file -match "^rename from (.*)$") {
+    $beforeRenameFiles += $file -replace "^rename from (.*)$", '$1'
+  }
+}
+# A combined list of deleted and renamed files.
+$relativePathLinks = ($deletedFiles + $beforeRenameFiles)
+# Removed the deleted markdowns. 
+$changedMarkdowns = $changedMarkdowns | Where-Object { $deletedFiles -notcontains $_ }
+# Scan all markdowns and find if it contains the deleted or renamed files.
+$markdownContainLinks = @()
+$allMarkdownFiles = Get-ChildItem -Path $RootRepo -Recurse -Include *.md
+foreach ($f in $allMarkdownFiles) {
+  $filePath = $f.FullName
+  $content = Get-Content -Path $filePath -Raw
+  foreach ($l in $relativePathLinks) {
+    if ($content -match $l) {
+      $markdownContainLinks += $filePath
+      break
+    }
+  }
+}
+
+# Convert markdowns path of the PR to absolute path.
+$adjustedReadmes = $changedMarkdowns | Foreach-Object { Resolve-Path $_ }
+$markdownContainLinks += $adjustedReadmes
+
+# Get rid of any duplicated ones.
+$allMarkdowns = [string[]]($markdownContainLinks | Sort-Object | Get-Unique)
+
+Write-Host "Here are all markdown files we need to check based on the changed files:"
+foreach ($file in $allMarkdowns) {
+  Write-Host "    $file"
+}
+return $allMarkdowns