Add histogram attributing cause of main thread scrolling.

CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

BUG=569077

Review URL: https://codereview.chromium.org/1484913002

Cr-Commit-Position: refs/heads/master@{#370057}

2 files changed, 57 insertions, 4 deletions

diff --git a/cc/blink/web_layer_impl.cc b/cc/blink/web_layer_impl.cc
index 88601b5..56c2af9 100644
--- a/cc/blink/web_layer_impl.cc
+++ b/cc/blink/web_layer_impl.cc
@@ -345,9 +345,58 @@ bool WebLayerImpl::haveScrollEventHandlers() const {
   return layer_->have_scroll_event_handlers();
 }
 
-void WebLayerImpl::setShouldScrollOnMainThread(
-    bool should_scroll_on_main_thread) {
-  layer_->SetShouldScrollOnMainThread(should_scroll_on_main_thread);
+static_assert(static_cast<cc::InputHandler::MainThreadScrollingReason>(
+                  blink::WebMainThreadScrollingReason::NotScrollingOnMain) ==
+                  cc::InputHandler::NOT_SCROLLING_ON_MAIN,
+              "InputHandler::MainThreadScrollingReason and "
+              "WebMainThreadScrollingReason enums must match");
+static_assert(static_cast<cc::InputHandler::MainThreadScrollingReason>(
+                  blink::WebMainThreadScrollingReason::
+                      HasBackgroundAttachmentFixedObjects) ==
+                  cc::InputHandler::HAS_BACKGROUND_ATTACHMENT_FIXED_OBJECTS,
+              "InputHandler::MainThreadScrollingReason and "
+              "WebMainThreadScrollingReason enums must match");
+static_assert(static_cast<cc::InputHandler::MainThreadScrollingReason>(
+                  blink::WebMainThreadScrollingReason::
+                      HasNonLayerViewportConstrainedObjects) ==
+                  cc::InputHandler::HAS_NON_LAYER_VIEWPORT_CONSTRAINED_OBJECTS,
+              "InputHandler::MainThreadScrollingReason and "
+              "WebMainThreadScrollingReason enums must match");
+static_assert(
+    static_cast<cc::InputHandler::MainThreadScrollingReason>(
+        blink::WebMainThreadScrollingReason::ThreadedScrollingDisabled) ==
+        cc::InputHandler::THREADED_SCROLLING_DISABLED,
+    "InputHandler::MainThreadScrollingReason and "
+    "WebMainThreadScrollingReason enums must match");
+static_assert(static_cast<cc::InputHandler::MainThreadScrollingReason>(
+                  blink::WebMainThreadScrollingReason::ScrollBarScrolling) ==
+                  cc::InputHandler::SCROLL_BAR_SCROLLING,
+              "InputHandler::MainThreadScrollingReason and "
+              "WebMainThreadScrollingReason enums must match");
+static_assert(static_cast<cc::InputHandler::MainThreadScrollingReason>(
+                  blink::WebMainThreadScrollingReason::PageOverlay) ==
+                  cc::InputHandler::PAGE_OVERLAY,
+              "InputHandler::MainThreadScrollingReason and "
+              "WebMainThreadScrollingReason enums must match");
+
+void WebLayerImpl::addMainThreadScrollingReasons(
+    blink::WebMainThreadScrollingReason::WebMainThreadScrollingReason
+        main_thread_scrolling_reasons) {
+  DCHECK(main_thread_scrolling_reasons);
+  // WebLayerImpl should only know about non-transient scrolling
+  // reasons. Transient scrolling reasons are computed per hit test.
+  DCHECK_LE(
+      main_thread_scrolling_reasons,
+      static_cast<
+          blink::WebMainThreadScrollingReason::WebMainThreadScrollingReason>(
+          cc::InputHandler::MaxNonTransientScrollingReason));
+  layer_->AddMainThreadScrollingReasons(
+      static_cast<cc::InputHandler::MainThreadScrollingReason>(
+          main_thread_scrolling_reasons));
+}
+
+void WebLayerImpl::clearMainThreadScrollingReasons() {
+  layer_->ClearMainThreadScrollingReasons();
 }
 
 bool WebLayerImpl::shouldScrollOnMainThread() const {
diff --git a/cc/blink/web_layer_impl.h b/cc/blink/web_layer_impl.h
index 3fd0bcc..482c633 100644
--- a/cc/blink/web_layer_impl.h
+++ b/cc/blink/web_layer_impl.h
@@ -22,6 +22,7 @@
 #include "third_party/WebKit/public/platform/WebDoublePoint.h"
 #include "third_party/WebKit/public/platform/WebFloatPoint.h"
 #include "third_party/WebKit/public/platform/WebLayer.h"
+#include "third_party/WebKit/public/platform/WebMainThreadScrollingReason.h"
 #include "third_party/WebKit/public/platform/WebPoint.h"
 #include "third_party/WebKit/public/platform/WebRect.h"
 #include "third_party/WebKit/public/platform/WebSize.h"
@@ -128,7 +129,10 @@ class WebLayerImpl : public blink::WebLayer {
   bool haveWheelEventHandlers() const override;
   void setHaveScrollEventHandlers(bool have_scroll_event_handlers) override;
   bool haveScrollEventHandlers() const override;
-  void setShouldScrollOnMainThread(bool scroll_on_main) override;
+  void addMainThreadScrollingReasons(
+      blink::WebMainThreadScrollingReason::WebMainThreadScrollingReason
+          main_thread_scrolling_reasons) override;
+  void clearMainThreadScrollingReasons() override;
   bool shouldScrollOnMainThread() const override;
   void setNonFastScrollableRegion(
       const blink::WebVector<blink::WebRect>& region) override;