performance measurement improvements and README update

pkg/analysis_server/benchmark/integration/README.md

Index: pkg/analysis_server/benchmark/integration/README.md
diff --git a/pkg/analysis_server/benchmark/integration/README.md b/pkg/analysis_server/benchmark/integration/README.md
index 7dc2180eb385a50b4012820fe4c2bdadc01f2d85..78431f91d5c0ecb2006eb33b7e40a8bae43793f1 100644
--- a/pkg/analysis_server/benchmark/integration/README.md
+++ b/pkg/analysis_server/benchmark/integration/README.md
@@ -12,12 +12,22 @@ This Dart application is one example for running performance benchmarks.
 When run, this application 1) extracts a branch from a git repository
 into a temporary directory, and 2) creates a symlink to the out or xcodebuild
 directory for proper package-root package resolution.
+Once setup is complete, this applications calls main.dart
+
 The required command line arguments are
 * **gitDir** = a path to the git repository containing the initial target source
 * **branch** = the branch containing the initial target source
 * **inputFile** = the instrumentation or log file
 
-Once setup is complete, this applications calls main.dart
+Additional arguments are passed directly to main.dart.
+For example, you may want to specify --newTaskModel to measure performance
+with the new task model versus the old task model,
+or if the log was recorded on one machine and is played back on another,
+then you might need to specify -m<oldSrcPath>,<newSrcPath>
+to map the source paths for playback.
+When specifying additional arguments, any occurrences of @tmpSrcDir@
+will be replaced with the absolute path of the temporary directory
+into which the source was extracted.
 
 ## main.dart
 
@@ -45,3 +55,18 @@ WARNING: The contents of the target directory will be modified
 *  **-v, --verbose**        Verbose logging
 *  **--vv**                 Extra verbose logging
 *  **-h, --help**           Print this help information
+
+For each request recorded in the input file,
+the application sends a corresponding request to the analysis server
+and waits up to 60 seconds for a response to that request.
+If a response in not received in that time, then the application exits.
+Any responses that are received are compared with the recorded response.
+
+For each analysis-complete notification recorded in the input file,
+the application waits for the corresponding analysis-complete notification
+from the running analysis server.
+While it is waiting for an analysis-complete notification,
+the application monitors the stream of notifications.
+If there is a period of more than 60 seconds during which no communication
+is received from the server, the application assumes that the server is hung
+and exits.