Touch emulator: enables double tap support for pages similar to Chrome on Android.

content/browser/renderer_host/frame_metadata_util.cc

+// Copyright (c) 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "content/browser/renderer_host/frame_metadata_util.h"
+
+#include "cc/output/compositor_frame_metadata.h"
+
+namespace {
+
+// Used to accomodate finite precision when comparing scaled viewport and
+// content widths. While this value may seem large, width=device-width on an N7
+// V1 saw errors of ~0.065 between computed window and content widths.
+const float kMobileViewportWidthEpsilon = 0.15f;
+
+bool HasFixedPageScale(const cc::CompositorFrameMetadata& frame_metadata) {
+  return frame_metadata.min_page_scale_factor ==
+         frame_metadata.max_page_scale_factor;
+}
+
+bool HasMobileViewport(const cc::CompositorFrameMetadata& frame_metadata) {
+  float window_width_dip =
+      frame_metadata.page_scale_factor *
+          frame_metadata.scrollable_viewport_size.width();
+  float content_width_css = frame_metadata.root_layer_size.width();
+  return content_width_css <= window_width_dip + kMobileViewportWidthEpsilon;
+}
+
+}  // namespace
+
+namespace content {
+
+bool IsMobileOptimizedFrame(const cc::CompositorFrameMetadata& frame_metadata) {
+  bool has_mobile_viewport = HasMobileViewport(frame_metadata);
+  bool has_fixed_page_scale = HasFixedPageScale(frame_metadata);
+  return has_fixed_page_scale || has_mobile_viewport;
+}
+
+}  // namespace content