renderer: Have the viewport meta element establish the initial zoom of new pages (#37315)

This patch contains 2 components: 

1. Instead of passing `self.pinch_zoom_level().get()` while checking
`zoom_result`, initialize it in `combined_magnification`. Ideally, this
part shouldn't have any effect on behavior.

2. Separates the logic for PinchZoom and ViewportZoom. So, when a new
page is opened, it will start with its own viewport zoom scale (rather
than the previous scale multiples).
i.e `self.pinch_zoom_level().get() * 1.0 * magnification`
```rust
        let mut combined_magnification = 1.0;
        ... 
                ScrollZoomEvent::ViewportZoom(magnification) => {
                    combined_magnification *= magnification
                },
        ...        
        let pinch_zoom_result = match self.set_pinch_zoom_level(self.pinch_zoom_level().get() * combined_magnification)
``` 





Testing: This change adds a new WPT test.
Fixes: #37314

---------

Signed-off-by: Shubham Gupta <shubham13297@gmail.com>

components/compositing/webview_renderer.rs

@@ -44,8 +44,8 @@ struct ScrollEvent {
 enum ScrollZoomEvent {
     /// A pinch zoom event that magnifies the view by the given factor.
     PinchZoom(f32),
-    /// A zoom event that magnifies the view by the factor parsed from meta tag.
+    /// A zoom event that establishes the initial zoom from the viewport meta tag.
-    ViewportZoom(f32),
+    InitialViewportZoom(f32),
     /// A scroll event that scrolls the scroll node at the given location by the
     /// given amount.
     Scroll(ScrollEvent),
@@ -799,13 +799,16 @@ impl WebViewRenderer {
 
         // Batch up all scroll events into one, or else we'll do way too much painting.
         let mut combined_scroll_event: Option<ScrollEvent> = None;
+        let mut base_page_zoom = self.pinch_zoom_level().get();
         let mut combined_magnification = 1.0;
         for scroll_event in self.pending_scroll_zoom_events.drain(..) {
             match scroll_event {
-                ScrollZoomEvent::PinchZoom(magnification) |
+                ScrollZoomEvent::PinchZoom(magnification) => {
-                ScrollZoomEvent::ViewportZoom(magnification) => {
                     combined_magnification *= magnification
                 },
+                ScrollZoomEvent::InitialViewportZoom(magnification) => {
+                    base_page_zoom = magnification
+                },
                 ScrollZoomEvent::Scroll(scroll_event_info) => {
                     let combined_event = match combined_scroll_event.as_mut() {
                         None => {
@@ -862,12 +865,11 @@ impl WebViewRenderer {
             );
         }
 
-        let pinch_zoom_result = match self
+        let pinch_zoom_result =
-            .set_pinch_zoom_level(self.pinch_zoom_level().get() * combined_magnification)
+            match self.set_pinch_zoom_level(base_page_zoom * combined_magnification) {
-        {
+                true => PinchZoomResult::DidPinchZoom,
-            true => PinchZoomResult::DidPinchZoom,
+                false => PinchZoomResult::DidNotPinchZoom,
-            false => PinchZoomResult::DidNotPinchZoom,
+            };
-        };
 
         (pinch_zoom_result, scroll_result)
     }
@@ -1035,7 +1037,7 @@ impl WebViewRenderer {
 
     pub fn set_viewport_description(&mut self, viewport_description: ViewportDescription) {
         self.pending_scroll_zoom_events
-            .push(ScrollZoomEvent::ViewportZoom(
+            .push(ScrollZoomEvent::InitialViewportZoom(
                 viewport_description
                     .clone()
                     .clamp_zoom(viewport_description.initial_scale.get()),

tests/wpt/meta/MANIFEST.json

@@ -373460,6 +373460,21 @@
      }
     }
    },
+   "visual-viewport": {
+    "viewport-apply-initial-scale-after-navigation.html": [
+     "ec03c380d6d27ed0b486a26203d441dc101fd39f",
+     [
+      null,
+      [
+       [
+        "/visual-viewport/viewport-apply-initial-scale-after-navigation-ref.html",
+        "=="
+       ]
+      ],
+      {}
+     ]
+    ]
+   },
    "web-animations": {
     "animation-model": {
      "keyframe-effects": {
@@ -522286,6 +522301,16 @@
      "c036b16ec87bc7e562c4040ad1923c5a8b483cec",
      []
     ],
+    "resource": {
+     "viewport-apply-initial-scale-after-navigation-inner.html": [
+      "edbf5dbb70aa916363ff32eab847f2d03562d4f5",
+      []
+     ]
+    },
+    "viewport-apply-initial-scale-after-navigation-ref.html": [
+     "904d370d6b464ef526b79e3974532d3f2c57d13b",
+     []
+    ],
     "viewport_support.js": [
      "a82bd2b028010e053199e55bd7bb357361581e6f",
      []

tests/wpt/tests/visual-viewport/resource/viewport-apply-initial-scale-after-navigation-inner.html

@@ -0,0 +1,16 @@
+<!DOCTYPE html>
+<html class="reftest-wait">
+    <head>
+        <title>Viewport: Apply initial-scale after Navigation</title>
+        <meta charset="utf-8">
+        <meta name="viewport" content="width=device-width, initial-scale=1.0">
+        <script src="/common/reftest-wait.js"></script>
+        <script>
+            onload = takeScreenshot;
+        </script>
+    </head>
+    <body>
+        <h1>Viewport: Apply initial-scale after Navigation</h1>
+        <p>Test passes if page opens with own initial-scale of 1.0</p>
+    </body>
+</html>

tests/wpt/tests/visual-viewport/viewport-apply-initial-scale-after-navigation-ref.html

@@ -0,0 +1,12 @@
+<!DOCTYPE html>
+<html>
+    <head>
+        <title>Viewport: Apply initial-scale after Navigation</title>
+        <meta charset="utf-8">
+        <meta name="viewport" content="width=device-width, initial-scale=1.0">
+    </head>
+    <body>
+        <h1>Viewport: Apply initial-scale after Navigation</h1>
+        <p>Test passes if page opens with own initial-scale of 1.0</p>
+    </body>
+</html>

tests/wpt/tests/visual-viewport/viewport-apply-initial-scale-after-navigation.html

@@ -0,0 +1,17 @@
+<!DOCTYPE html>
+<html class="reftest-wait">
+<head>
+    <title>Viewport: Apply initial-scale after Navigation</title>
+    <meta charset="utf-8">
+    <meta name="viewport" content="width=device-width, initial-scale=2.0">
+    <link rel="match" href="viewport-apply-initial-scale-after-navigation-ref.html">
+    <script src="/common/reftest-wait.js"></script>
+    <script>
+        function runTest() {
+            const url = "resource/viewport-apply-initial-scale-after-navigation-inner.html";
+            window.location.replace(new URL(url, window.location));
+        }
+        onload = () => runTest();
+    </script>
+</head>
+</html>