[debugger] remove default count for top-level functions.

If the top-level function cannot be found, we previously assumed an
invocation count of 1. This is wrong when we expect the invocation
counts to be reset for precise coverage.

TBR=jgruber@chromium.org
R=caseq@chromium.org,pfeldman@chromium.org
BUG=v8:5808

Review-Url: https://codereview.chromium.org/2723003007
Cr-Commit-Position: refs/heads/master@{#43620}

src/debug/debug-coverage.cc

@@ -103,27 +103,16 @@ Coverage* Coverage::Collect(Isolate* isolate, bool reset_count) {
     std::vector<CoverageFunction>* functions = &result->back().functions;
 
     std::vector<SharedFunctionInfo*> sorted;
-    bool has_toplevel = false;
 
     {
       // Sort functions by start position, from outer to inner functions.
       SharedFunctionInfo::ScriptIterator infos(script_handle);
       while (SharedFunctionInfo* info = infos.Next()) {
-        has_toplevel |= info->is_toplevel();
         sorted.push_back(info);
       }
       std::sort(sorted.begin(), sorted.end(), CompareSharedFunctionInfo);
     }
 
-    functions->reserve(sorted.size() + (has_toplevel ? 0 : 1));
-
-    if (!has_toplevel) {
-      // Add a replacement toplevel function if it does not exist.
-      int source_end = String::cast(script->source())->length();
-      functions->emplace_back(0, source_end, 1u,
-                              isolate->factory()->empty_string());
-    }
-
     // Use sorted list to reconstruct function nesting.
     for (SharedFunctionInfo* info : sorted) {
       int start = StartPosition(info);

test/inspector/cpu-profiler/coverage-expected.txt

 Test collecting code coverage data with Profiler.collectCoverage.
 
+Running test: testPreciseBaseline
+{
+    id : <messageId>
+    result : {
+        result : [
+            [0] : {
+                functions : [
+                    [0] : {
+                        functionName : fib
+                        ranges : [
+                            [0] : {
+                                count : 0
+                                endColumnNumber : 1
+                                endLineNumber : 4
+                                startColumnNumber : 0
+                                startLineNumber : 1
+                            }
+                        ]
+                    }
+                ]
+                scriptId : <scriptId>
+                url : 0
+            }
+        ]
+    }
+}
+{
+    id : <messageId>
+    result : {
+        result : [
+            [0] : {
+                functions : [
+                    [0] : {
+                        functionName : fib
+                        ranges : [
+                            [0] : {
+                                count : 0
+                                endColumnNumber : 1
+                                endLineNumber : 4
+                                startColumnNumber : 0
+                                startLineNumber : 1
+                            }
+                        ]
+                    }
+                ]
+                scriptId : <scriptId>
+                url : 0
+            }
+        ]
+    }
+}
+
 Running test: testPreciseCoverage
 {
     id : <messageId>

test/inspector/cpu-profiler/coverage.js

@@ -17,8 +17,11 @@ fib(5);
 InspectorTest.log("Test collecting code coverage data with Profiler.collectCoverage.");
 
 function ClearAndGC() {
-  return Protocol.Runtime.evaluate({ expression: "fib = null;" })
-           .then(() => Protocol.HeapProfiler.enable())
+  return Protocol.Runtime.evaluate({ expression: "fib = null;" }).then(GC);
+}
+
+function GC() {
+  return Protocol.HeapProfiler.enable()
            .then(() => Protocol.HeapProfiler.collectGarbage())
            .then(() => Protocol.HeapProfiler.disable());
 }
@@ -29,6 +32,24 @@ function LogSorted(message) {
 }
 
 InspectorTest.runTestSuite([
+  function testPreciseBaseline(next)
+  {
+    Protocol.Runtime.enable()
+      .then(() => Protocol.Runtime.compileScript({ expression: source, sourceURL: "0", persistScript: true }))
+      .then((result) => Protocol.Runtime.runScript({ scriptId: result.result.scriptId }))
+      .then(GC)
+      .then(Protocol.Profiler.enable)
+      .then(Protocol.Profiler.startPreciseCoverage)
+      .then(Protocol.Profiler.takePreciseCoverage)
+      .then(LogSorted)
+      .then(Protocol.Profiler.takePreciseCoverage)
+      .then(LogSorted)
+      .then(Protocol.Profiler.stopPreciseCoverage)
+      .then(ClearAndGC)
+      .then(Protocol.Profiler.disable)
+      .then(Protocol.Runtime.disable)
+      .then(next);
+  },
   function testPreciseCoverage(next)
   {
     Protocol.Runtime.enable()