Enable V8 idle tasks.

Source/bindings/core/v8/V8Initializer.cpp

Index: Source/bindings/core/v8/V8Initializer.cpp
diff --git a/Source/bindings/core/v8/V8Initializer.cpp b/Source/bindings/core/v8/V8Initializer.cpp
index f73978540a245000a78a8a178ab3b90a6fb93a5a..14e6c037d5bf4069c88ee354e8b039435b041771 100644
--- a/Source/bindings/core/v8/V8Initializer.cpp
+++ b/Source/bindings/core/v8/V8Initializer.cpp
@@ -47,7 +47,9 @@
 #include "core/frame/csp/ContentSecurityPolicy.h"
 #include "core/inspector/ScriptCallStack.h"
 #include "platform/EventDispatchForbiddenScope.h"
+#include "platform/RuntimeEnabledFeatures.h"
 #include "platform/TraceEvent.h"
+#include "platform/scheduler/Scheduler.h"
 #include "public/platform/Platform.h"
 #include "wtf/RefPtr.h"
 #include "wtf/text/WTFString.h"
@@ -178,6 +180,32 @@ static bool codeGenerationCheckCallbackInMainThread(v8::Local<v8::Context> conte
     return false;
 }
 
+static void idleGCTaskInMainThread(double deadlineSeconds);
+
+static void postIdleGCTaskMainThread()
+{
+    if (RuntimeEnabledFeatures::v8IdleTasksEnabled()) {
+        Scheduler* scheduler = Scheduler::shared();
+        if (scheduler)
+            scheduler->postIdleTask(FROM_HERE, WTF::bind<double>(idleGCTaskInMainThread));
+    }
+}
+
+static void idleGCTaskInMainThread(double deadlineSeconds)
+{
+    ASSERT(isMainThread());
+    ASSERT(RuntimeEnabledFeatures::v8IdleTasksEnabled());
+    v8::Isolate* isolate = v8::Isolate::GetCurrent();
+    // TODO: Change V8's API to take a deadline - http://crbug.com/417668

[jochen (gone - plz use gerrit), 2014/10/13 08:06:20]

blink has FIXME: instead of TODO

[rmcilroy, 2014/10/13 11:22:07]

Done.

+    double idleTimeInSeconds = deadlineSeconds - Platform::current()->monotonicallyIncreasingTime();
+    int idleTimeInMillis = static_cast<int>(idleTimeInSeconds * 1000);
+    if (idleTimeInMillis > 0) {

[jochen (gone - plz use gerrit), 2014/10/13 08:06:20]

no { } required

[jochen (gone - plz use gerrit), 2014/10/13 08:06:20]

no { } required

[rmcilroy, 2014/10/13 11:22:08]

Done.

+        isolate->IdleNotification(idleTimeInMillis);
+    }
+    // TODO: only repost if there is more work to do.
+    postIdleGCTaskMainThread();

[jochen (gone - plz use gerrit), 2014/10/13 08:06:20]

how will you make sure that you don't end up squeezing multiple gc tasks into a
single idle pause.

how will you restart idle notifications once nothing more was to be done?

[rmcilroy, 2014/10/13 11:22:07]

CL https://codereview.chromium.org/640053003/ deals with this - it ensures that
only tasks posted before the current idle period will execute during the current
idle period.
This is what we will need to work out.  Is there any bottleneck on starting JS
execution which we could use for this?

+}
+
 static void timerTraceProfilerInMainThread(const char* name, int status)
 {
     if (!status) {