web-threads: Create a single instance of WebThread for each blink thread.

content/test/test_blink_web_unit_test_support.cc

Index: content/test/test_blink_web_unit_test_support.cc
diff --git a/content/test/test_blink_web_unit_test_support.cc b/content/test/test_blink_web_unit_test_support.cc
index 1bee8c053639a4ac4ec9670b050b86044058cf7e..81a0552b2ebddb2e8981356b68e17e0b99f289b0 100644
--- a/content/test/test_blink_web_unit_test_support.cc
+++ b/content/test/test_blink_web_unit_test_support.cc
@@ -13,6 +13,7 @@
 #include "content/public/common/content_switches.h"
 #include "content/renderer/scheduler/renderer_scheduler.h"
 #include "content/renderer/scheduler/web_scheduler_impl.h"
+#include "content/renderer/scheduler/webthread_impl_for_scheduler.h"
 #include "content/test/mock_webclipboard_impl.h"
 #include "content/test/web_gesture_curve_mock.h"
 #include "content/test/web_layer_tree_view_impl_for_testing.h"
@@ -60,6 +61,7 @@ TestBlinkWebUnitTestSupport::TestBlinkWebUnitTestSupport() {
   if (base::MessageLoopProxy::current()) {
     renderer_scheduler_ = RendererScheduler::Create();
     web_scheduler_.reset(new WebSchedulerImpl(renderer_scheduler_.get()));
+    web_thread_.reset(new WebThreadImplForScheduler(renderer_scheduler_.get()));
   }
 
   blink::initialize(this);
@@ -319,4 +321,10 @@ blink::WebScheduler* TestBlinkWebUnitTestSupport::scheduler() {
   return web_scheduler_.get();
 }
 
+blink::WebThread* TestBlinkWebUnitTestSupport::currentThread() {

[Sami, 2015/03/02 11:40:02]

I'm wondering if we should just register web_thread_ into the TLS instead of
overriding this method here (and doing the same in RendererBlinkPlatformImpl)?
That would require a little less special casing, but then again TLS lookups can
be slow on some platforms. WDYT?

[sadrul, 2015/03/02 16:53:21]

From our earlier discussion
(https://codereview.chromium.org/959803003/diff/180001/content/child/blink_pla...),
it may be possible to just get rid of the TLS we maintain in BlinkPlatformImpl
since currentThread() is only called on main-thread. In that case, we would need
overrides in both RendererBlinkPlatformImpl and here.

[Sami, 2015/03/02 17:25:06]

Interesting. Maybe that code should be migrated to this:

https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...

(Note: I'm in the middle of moving clients of WTF::callOnMain to that too.)

+  if (web_thread_ && web_thread_->isCurrentThread())
+    return web_thread_.get();
+  return BlinkPlatformImpl::currentThread();
+}
+
 }  // namespace content