Implement fullPage screenshots

This patch adds a 'fullPage' option to the Page.screenshot
method.

Fixes #6.

lib/Page.js

@@ -401,14 +401,11 @@ class Page extends EventEmitter {
                 screenshotType = 'png';
             else if (mimeType === 'image/jpeg')
                 screenshotType = 'jpeg';
-            else
+            console.assert(screenshotType, 'Unsupported screenshot mime type: ' + mimeType);
-                throw new Error('Unsupported screenshot mime type: ' + mimeType);
         }
         if (options.type) {
-            if (screenshotType && options.type !== screenshotType)
+            console.assert(!screenshotType || options.type === screenshotType, `Passed screenshot type '${options.type}' does not match the type inferred from the file path: '${screenshotType}'`);
-                throw new Error(`Passed screenshot type '${options.type}' does not match to the type inferred from the file path: '${screenshotType}'`);
+            console.assert(options.type === 'png' || options.type === 'jpeg', 'Unknown options.type value: ' + options.type);
-            if (options.type !== 'png' && options.type !== 'jpeg')
-                throw new Error('Unknown screenshot type: ' + options.type);
             screenshotType = options.type;
         }
         if (!screenshotType)
@@ -420,6 +417,7 @@ class Page extends EventEmitter {
             console.assert(Number.isInteger(options.quality), 'Expected options.quality to be an integer');
             console.assert(options.quality >= 0 && options.quality <= 100, 'Expected options.quality to be between 0 and 100 (inclusive), got ' + options.quality);
         }
+        console.assert(!options.clip || !options.fullPage, 'options.clip and options.fullPage are exclusive');
         if (options.clip) {
             console.assert(typeof options.clip.x === 'number', 'Expected options.clip.x to be a number but found ' + (typeof options.clip.x));
             console.assert(typeof options.clip.y === 'number', 'Expected options.clip.y to be a number but found ' + (typeof options.clip.y));
@@ -448,13 +446,26 @@ class Page extends EventEmitter {
                     scale: 1,
                 })
             ]);
+        } else if (options.fullPage) {
+            var response = await this._client.send('Page.getLayoutMetrics');
+            await Promise.all([
+                this._client.send('Emulation.setVisibleSize', {
+                    width: Math.ceil(response.contentSize.width / this._screenDPI),
+                    height: Math.ceil(response.contentSize.height / this._screenDPI),
+                }),
+                this._client.send('Emulation.forceViewport', {
+                    x: 0,
+                    y: 0,
+                    scale: 1,
+                })
+            ]);
         }
         var result = await this._client.send('Page.captureScreenshot', {
             fromSurface: true,
             format: screenshotType,
             quality: options.quality
         });
-        if (options.clip) {
+        if (options.clip || options.fullPage) {
             await Promise.all([
                 this.setViewportSize(this.viewportSize()),
                 this._client.send('Emulation.resetViewport')

test/test.js

@@ -258,6 +258,14 @@ describe('Puppeteer', function() {
             var screenshot = await promises[1];
             expect(screenshot).toBeGolden('screenshot-parallel-calls.png');
         }));
+        it('should take fullPage screenshots', SX(async function() {
+            await page.setViewportSize({width: 500, height: 500});
+            await page.navigate(STATIC_PREFIX + '/grid.html');
+            var screenshot = await page.screenshot({
+                fullPage: true
+            });
+            expect(screenshot).toBeGolden('screenshot-grid-fullpage.png');
+        }));
     });
 });