Do nothing if [changeFile] reported, but the file content is the same.

pkg/analyzer/lib/src/dart/analysis/driver.dart

Index: pkg/analyzer/lib/src/dart/analysis/driver.dart
diff --git a/pkg/analyzer/lib/src/dart/analysis/driver.dart b/pkg/analyzer/lib/src/dart/analysis/driver.dart
index 6677376eb6194c04a09169e52b31f29eb282102f..443b0517a443670944260bb3be23b418e39686c4 100644
--- a/pkg/analyzer/lib/src/dart/analysis/driver.dart
+++ b/pkg/analyzer/lib/src/dart/analysis/driver.dart
@@ -208,12 +208,6 @@ class AnalysisDriver {
    * "analyzing" and an analysis result is produced for every added file prior
    * to the next time the analysis state transitions to "idle".
    *
-   * At least one analysis result is produced for every file passed to
-   * [addFile] or [changeFile] prior to the next time the analysis state
-   * transitions to "idle", unless the file is later removed from analysis
-   * using [removeFile]. Analysis results for other files are produced only if
-   * the changes affect analysis results of other files.
-   *
    * More than one result might be produced for the same file, even if the
    * client does not change the state of the files.
    *
@@ -305,6 +299,11 @@ class AnalysisDriver {
    * The [path] must be absolute and normalized.
    *
    * The results of analysis are eventually produced by the [results] stream.
+   *
+   * Causes the analysis state to transition to "analyzing" (if it is not in
+   * that state already). At least one analysis result will be produced the
+   * file prior to the next time the analysis state transitions to "idle",
+   * unless the file is later removed from analysis using [removeFile].
    */
   void addFile(String path) {
     _explicitFiles.add(path);
@@ -326,6 +325,11 @@ class AnalysisDriver {
    * into the current file state prior to the next time the analysis state
    * transitions to "idle".
    *
+   * If the file content is the same, no new results will be produced because
+   * of this notification, including no result for the file itself. Otherwise,
+   * one or more results will be produced - for the file itself and other
+   * files that that change in the file might affect.

[Brian Wilkerson, 2016/10/31 14:06:04]

"that that" --> "that the"

+   *
    * Invocation of this method will not prevent a [Future] returned from
    * [getResult] from completing with a result, but the result is not
    * guaranteed to be consistent with the new current file state after this
@@ -681,16 +685,22 @@ class AnalysisDriver {
    */
   void _verifyApiSignatureOfChangedFile(String path) {
     _logger.run('Verify API signature of $path', () {
+      String oldContentHash = _fileContentHashMap[path];
       String oldSignature = _fileApiSignatureMap[path];
       // Compute the new API signature.
       // _File.forResolution() also updates the content hash in the cache.
       Source source = _sourceForPath(path);
       _File newFile = new _File.forResolution(this, source);
-      String newSignature = newFile.unlinked.apiSignature;
+      // If the file content hash is the same, we don't need analyzing it.

[Brian Wilkerson, 2016/10/31 14:06:04]

"need analyzing it" --> "need to analyze it"

+      if (newFile.contentHash == oldContentHash) {
+        _filesToAnalyze.remove(path);
+        return;
+      }
       // If the old API signature is not null, then the file was used to
       // compute at least one dependency signature. If the new API signature
       // is different, then potentially all dependency signatures and
       // resolution results are invalid.
+      String newSignature = newFile.unlinked.apiSignature;
       if (oldSignature != null && oldSignature != newSignature) {
         _logger.writeln('API signatures mismatch found for $newFile');
         _dependencySignatureMap.clear();