Changes in this patch are as below:
1. chrome_elf: Removing breakpad and corresponding exception initialization using breakpad. Registering
   crashpad as the exception handling mechanism in chrome_elf. We continue to handle exceptions in chrome_elf
   DllMain and in the blacklist interception code as before, i.e. we use crashpad to grab the dump and pass
   the exception to the next handler in the chain. I also added support in chrome_elf to not initialize
   crashpad if it is being loaded in some tests. For e.g. the ELFImportsTest. This is via the exe name check.

2. chrome.exe:- Removing crashpad exception registration. Also we need to retrieve current exception reports information
   from chrome_elf instead of chrome.

3. Intercept the SetUnhandledExceptionFilter API in chrome_elf via IAT patching on the exe and disallow the call. This
   is to prevent CRT from overwriting crashpads exception filter. I added a TODO to see if we can use EAT patching or
   possibly sidestep if we can support 64 bit with it.

4. Added a function RegisterCrashKeysForDebugging to the ChromeCrashReporterClient class on Windows
   to register crash keys. This is currently invoked from chrome_elf for debugging purposes.

5. Changed the browser lib target to depend on chrome_elf:blacklist instead of chrome_elf. This prevents chrome_elf
   from being implicitly loaded in processes other than chrome.exe

BUG=604923,crashpad:106, 568664
TBR=robertshield

Review-Url: https://codereview.chromium.org/2088133002
Cr-Commit-Position: refs/heads/master@{#403048}