Adding streamz metrics to Java agent

Adding same counters as for C++ (in CL/149973373). For Java, we are running inside of web server.

Making sure streamz is not part of GAE (b/36560056)

Running the following tap_presubmit to cover apphosting testing:

tap_presubmit -p cloud_debugger,apphosting,apphosting.java,apphosting.java7_piii,apphosting.java8,apphosting.prod_config,apphosting.prod_config.appengine,apphosting.sandman_flag_tests,apphosting.servinf -c 151850960

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=152066844

Author: maximgoldin

src/agent/jvm_breakpoint.cc

@@ -33,6 +33,7 @@
 #include "resolved_source_location.h"
 #include "statistician.h"
 
+
 DEFINE_FLAG(
     int32,
     breakpoint_expiration_sec,
@@ -784,7 +785,8 @@ void JvmBreakpoint::CompleteBreakpoint(
     BreakpointBuilder* builder,
     std::unique_ptr<CaptureDataCollector> collector) {
   builder->set_is_final_state(true);
-  format_queue_->Enqueue(builder->build(), std::move(collector));
+  std::unique_ptr<BreakpointModel> model = builder->build();
+  format_queue_->Enqueue(std::move(model), std::move(collector));
 
   breakpoints_manager_->CompleteBreakpoint(id());
 

src/agent/model.h

@@ -62,6 +62,20 @@ struct StatusMessageModel {
            (refers_to == other.refers_to) &&
            (description == other.description);
   }
+
+  string RefersToToString() const {
+    switch (refers_to) {
+      case Context::UNSPECIFIED : return "UNSPECIFIED";
+      case Context::BREAKPOINT_SOURCE_LOCATION :
+        return "BREAKPOINT_SOURCE_LOCATION";
+      case Context::BREAKPOINT_CONDITION : return "BREAKPOINT_CONDITION";
+      case Context::BREAKPOINT_EXPRESSION : return "BREAKPOINT_EXPRESSION";
+      case Context::BREAKPOINT_AGE : return "BREAKPOINT_AGE";
+      case Context::VARIABLE_NAME : return "VARIABLE_NAME";
+      case Context::VARIABLE_VALUE : return "VARIABLE_VALUE";
+      default : return "UNKNOWN";
+    }
+  }
 };
 
 struct SourceLocationModel {
@@ -97,6 +111,14 @@ struct BreakpointModel {
     ERROR = 2
   };
 
+  string ActionToString() const {
+    switch (action) {
+      case Action::CAPTURE : return "CAPTURE";
+      case Action::LOG : return "LOG";
+      default : return "UNKNOWN";
+    }
+  }
+
   string id;
   bool is_canary = false;
   Action action = Action::CAPTURE;