Make possible to don't track cache dependencies.

If 'trackCacheDependencies' is set to 'false', this makes DDC
compilation of Angular2 project about 10% faster.

Unfortunately I was not able to avoid creating ResultDescriptor(s) and
adding them into WorkItem.inputTargetedResults altogether. It is used
in AnalysisTask._findCyclicPath() to create InfiniteTaskLoopException
with additional information.

R=brianwilkerson@google.com, paulberry@google.com
BUG=

Review URL: https://codereview.chromium.org/2054453002 .

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

@@ -298,6 +298,7 @@ class AnalysisContextImpl implements InternalAnalysisContext {
     this._options.lint = options.lint;
     this._options.preserveComments = options.preserveComments;
     this._options.strongMode = options.strongMode;
+    this._options.trackCacheDependencies = options.trackCacheDependencies;
     if (options is AnalysisOptionsImpl) {
       this._options.strongModeHints = options.strongModeHints;
     }

pkg/analyzer/lib/src/generated/engine.dart

@@ -1143,6 +1143,14 @@ abstract class AnalysisOptions {
    */
   bool get strongMode;
 
+  /**
+   * Return `true` if dependencies between computed results should be tracked
+   * by analysis cache.  This option should only be set to `false` if analysis
+   * is performed in such a way that none of the inputs is ever changed
+   * during the life time of the context.
+   */
+  bool get trackCacheDependencies;
+
   /**
    * Return an integer encoding of the values of the options that need to be the
    * same across all of the contexts associated with partitions that are to be
@@ -1283,6 +1291,9 @@ class AnalysisOptionsImpl implements AnalysisOptions {
   // TODO(leafp): replace this with something more general
   bool strongModeHints = false;
 
+  @override
+  bool trackCacheDependencies = true;
+
   /**
    * Initialize a newly created set of analysis options to have their default
    * values.
@@ -1315,6 +1326,7 @@ class AnalysisOptionsImpl implements AnalysisOptions {
     if (options is AnalysisOptionsImpl) {
       strongModeHints = options.strongModeHints;
     }
+    trackCacheDependencies = options.trackCacheDependencies;
   }
 
   bool get analyzeFunctionBodies {

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

@@ -278,7 +278,10 @@ class AnalysisDriver {
       AnalysisTarget target = task.target;
       CacheEntry entry = context.getCacheEntry(target);
       if (task.caughtException == null) {
-        List<TargetedResult> dependedOn = item.inputTargetedResults.toList();
+        List<TargetedResult> dependedOn =
+            context.analysisOptions.trackCacheDependencies
+                ? item.inputTargetedResults.toList()
+                : const <TargetedResult>[];
         Map<ResultDescriptor, dynamic> outputs = task.outputs;
         List<ResultDescriptor> results = task.descriptor.results;
         int resultLength = results.length;

pkg/analyzer/test/src/task/driver_test.dart

@@ -818,6 +818,9 @@ class _InternalAnalysisContextMock extends TypedMock
     implements InternalAnalysisContext {
   AnalysisCache analysisCache;
 
+  @override
+  final AnalysisOptionsImpl analysisOptions = new AnalysisOptionsImpl();
+
   @override
   List<AnalysisTarget> explicitTargets = <AnalysisTarget>[];