Add the analysis options path to the diagnostics page.

pkg/analyzer/lib/src/context/builder.dart

Index: pkg/analyzer/lib/src/context/builder.dart
diff --git a/pkg/analyzer/lib/src/context/builder.dart b/pkg/analyzer/lib/src/context/builder.dart
index 0b300e585e123bcdf0d72df4fe77e0f1b7ac02ca..c5eb63442cc9fd8c1ddc3e269d287296bdf7fe04 100644
--- a/pkg/analyzer/lib/src/context/builder.dart
+++ b/pkg/analyzer/lib/src/context/builder.dart
@@ -407,10 +407,12 @@ class ContextBuilder {
     AnalysisOptionsImpl options = createDefaultOptions();
     File optionsFile = getOptionsFile(path);
     Map<String, YamlNode> optionMap;
+    String optionsFilePath;
 
     if (optionsFile != null) {
       try {
         optionMap = optionsProvider.getOptionsFromFile(optionsFile);
+        optionsFilePath = optionsFile.path;
         verbose('Loaded analysis options from ${optionsFile.path}');
       } catch (e) {
         // Ignore exceptions thrown while trying to load the options file.
@@ -431,6 +433,7 @@ class ContextBuilder {
         if (source != null && source.exists()) {
           try {
             optionMap = optionsProvider.getOptionsFromSource(source);
+            optionsFilePath = source.fullName;
             verbose('Loaded analysis options from ${source.fullName}');
           } catch (e) {
             // Ignore exceptions thrown while trying to load the options file.
@@ -442,6 +445,7 @@ class ContextBuilder {
 
     if (optionMap != null) {
       applyToAnalysisOptions(options, optionMap);
+      options.optionsFilePath = optionsFilePath;
       if (builderOptions.argResults != null) {
         applyAnalysisOptionFlags(options, builderOptions.argResults,
             verbosePrint: verbosePrint);