Resolve paths against CWD in page.uploadFile() method

This patch:
- teaches page.uploadFile() to resolve given file paths against
  current working directory. This aligns paths handling with all the
  other methods
- moves page.uploadFile() under Frame
- changes test to use relative path for file upload

docs/api.md

@@ -90,6 +90,7 @@
     + [frame.name()](#framename)
     + [frame.parentFrame()](#frameparentframe)
     + [frame.title()](#frametitle)
+    + [frame.uploadFile(selector, ...filePaths)](#frameuploadfileselector-filepaths)
     + [frame.url()](#frameurl)
     + [frame.waitFor(selectorOrFunctionOrTimeout[, options])](#framewaitforselectororfunctionortimeout-options)
     + [frame.waitForFunction(pageFunction[, options, ...args])](#framewaitforfunctionpagefunction-options-args)
@@ -630,7 +631,7 @@ To press a special key, use [`page.press`](#pagepresskey-options).
 
 #### page.uploadFile(selector, ...filePaths)
 - `selector` <[string]> A query [selector] to a file input
-- `...filePaths` <[string]> Sets the value of the file input these paths
+- `...filePaths` <[string]> Sets the value of the file input these paths. If some of the  `filePaths` are relative paths, then they are resolved relative to [current working directory](https://nodejs.org/api/process.html#process_process_cwd).
 - returns: <[Promise]> Promise which resolves when the value is set.
 
 #### page.url()
@@ -900,6 +901,11 @@ Note: This value is calculated once when the frame is created, and will not upda
 #### frame.title()
 - returns: <[Promise]<[string]>> Returns page's title.
 
+#### frame.uploadFile(selector, ...filePaths)
+- `selector` <[string]> A query [selector] to a file input
+- `...filePaths` <[string]> Sets the value of the file input these paths. If some of the  `filePaths` are relative paths, then they are resolved relative to [current working directory](https://nodejs.org/api/process.html#process_process_cwd).
+- returns: <[Promise]> Promise which resolves when the value is set.
+
 #### frame.url()
 - returns: <[string]>
 

lib/FrameManager.js

@@ -15,6 +15,7 @@
  */
 
 let fs = require('fs');
+let path = require('path');
 let EventEmitter = require('events');
 let helper = require('./helper');
 
@@ -323,6 +324,21 @@ class Frame {
     return new WaitTask(this, predicateCode, polling, timeout).promise;
   }
 
+  /**
+   * @param {string} selector
+   * @param {!Array<string>} filePaths
+   * @return {!Promise}
+   */
+  async uploadFile(selector, ...filePaths) {
+    let expression = helper.evaluationString(selector => document.querySelector(selector), selector);
+    const {result} = await this._client.send('Runtime.evaluate', { expression });
+    if (!result)
+      return;
+    const objectId = result.objectId;
+    filePaths = filePaths.map(filePath => path.resolve(filePath));
+    return this._client.send('DOM.setFileInputFiles', { objectId, files: filePaths });
+  }
+
   /**
    * @template T
    * @param {string} selector

lib/Page.js

@@ -590,12 +590,7 @@ class Page extends EventEmitter {
    * @return {!Promise}
    */
   async uploadFile(selector, ...filePaths) {
-    let expression = helper.evaluationString(selector => document.querySelector(selector), selector);
-    const {result} = await this._client.send('Runtime.evaluate', { expression });
-    if (!result)
-      return;
-    const objectId = result.objectId;
-    return this._client.send('DOM.setFileInputFiles', { objectId, files: filePaths });
+    return this.mainFrame().uploadFile(selector, ...filePaths);
   }
 
   /**

test/test.js

@@ -875,7 +875,8 @@ describe('Puppeteer', function() {
     }));
     it('should upload the file', SX(async function(){
       await page.navigate(PREFIX + '/input/fileupload.html');
-      await page.uploadFile('input', __dirname + '/assets/file-to-upload.txt');
+      const filePath = path.relative(process.cwd(), __dirname + '/assets/file-to-upload.txt');
+      await page.uploadFile('input', filePath);
       expect(await page.evaluate(() => {
         let input = document.querySelector('input');
         return input.files[0].name;